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659 lines
22 KiB
659 lines
22 KiB
User Interface for Resource Allocation in Intel Resource Director Technology
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Copyright (C) 2016 Intel Corporation
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Fenghua Yu <fenghua.yu@intel.com>
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Tony Luck <tony.luck@intel.com>
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Vikas Shivappa <vikas.shivappa@intel.com>
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This feature is enabled by the CONFIG_INTEL_RDT Kconfig and the
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X86 /proc/cpuinfo flag bits "rdt", "cqm", "cat_l3" and "cdp_l3".
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To use the feature mount the file system:
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# mount -t resctrl resctrl [-o cdp] /sys/fs/resctrl
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mount options are:
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"cdp": Enable code/data prioritization in L3 cache allocations.
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RDT features are orthogonal. A particular system may support only
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monitoring, only control, or both monitoring and control.
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The mount succeeds if either of allocation or monitoring is present, but
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only those files and directories supported by the system will be created.
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For more details on the behavior of the interface during monitoring
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and allocation, see the "Resource alloc and monitor groups" section.
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Info directory
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--------------
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The 'info' directory contains information about the enabled
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resources. Each resource has its own subdirectory. The subdirectory
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names reflect the resource names.
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Each subdirectory contains the following files with respect to
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allocation:
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Cache resource(L3/L2) subdirectory contains the following files
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related to allocation:
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"num_closids": The number of CLOSIDs which are valid for this
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resource. The kernel uses the smallest number of
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CLOSIDs of all enabled resources as limit.
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"cbm_mask": The bitmask which is valid for this resource.
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This mask is equivalent to 100%.
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"min_cbm_bits": The minimum number of consecutive bits which
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must be set when writing a mask.
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"shareable_bits": Bitmask of shareable resource with other executing
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entities (e.g. I/O). User can use this when
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setting up exclusive cache partitions. Note that
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some platforms support devices that have their
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own settings for cache use which can over-ride
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these bits.
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Memory bandwitdh(MB) subdirectory contains the following files
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with respect to allocation:
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"min_bandwidth": The minimum memory bandwidth percentage which
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user can request.
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"bandwidth_gran": The granularity in which the memory bandwidth
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percentage is allocated. The allocated
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b/w percentage is rounded off to the next
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control step available on the hardware. The
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available bandwidth control steps are:
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min_bandwidth + N * bandwidth_gran.
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"delay_linear": Indicates if the delay scale is linear or
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non-linear. This field is purely informational
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only.
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If RDT monitoring is available there will be an "L3_MON" directory
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with the following files:
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"num_rmids": The number of RMIDs available. This is the
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upper bound for how many "CTRL_MON" + "MON"
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groups can be created.
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"mon_features": Lists the monitoring events if
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monitoring is enabled for the resource.
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"max_threshold_occupancy":
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Read/write file provides the largest value (in
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bytes) at which a previously used LLC_occupancy
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counter can be considered for re-use.
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Resource alloc and monitor groups
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---------------------------------
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Resource groups are represented as directories in the resctrl file
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system. The default group is the root directory which, immediately
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after mounting, owns all the tasks and cpus in the system and can make
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full use of all resources.
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On a system with RDT control features additional directories can be
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created in the root directory that specify different amounts of each
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resource (see "schemata" below). The root and these additional top level
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directories are referred to as "CTRL_MON" groups below.
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On a system with RDT monitoring the root directory and other top level
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directories contain a directory named "mon_groups" in which additional
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directories can be created to monitor subsets of tasks in the CTRL_MON
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group that is their ancestor. These are called "MON" groups in the rest
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of this document.
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Removing a directory will move all tasks and cpus owned by the group it
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represents to the parent. Removing one of the created CTRL_MON groups
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will automatically remove all MON groups below it.
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All groups contain the following files:
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"tasks":
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Reading this file shows the list of all tasks that belong to
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this group. Writing a task id to the file will add a task to the
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group. If the group is a CTRL_MON group the task is removed from
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whichever previous CTRL_MON group owned the task and also from
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any MON group that owned the task. If the group is a MON group,
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then the task must already belong to the CTRL_MON parent of this
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group. The task is removed from any previous MON group.
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"cpus":
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Reading this file shows a bitmask of the logical CPUs owned by
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this group. Writing a mask to this file will add and remove
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CPUs to/from this group. As with the tasks file a hierarchy is
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maintained where MON groups may only include CPUs owned by the
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parent CTRL_MON group.
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"cpus_list":
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Just like "cpus", only using ranges of CPUs instead of bitmasks.
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When control is enabled all CTRL_MON groups will also contain:
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"schemata":
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A list of all the resources available to this group.
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Each resource has its own line and format - see below for details.
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When monitoring is enabled all MON groups will also contain:
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"mon_data":
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This contains a set of files organized by L3 domain and by
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RDT event. E.g. on a system with two L3 domains there will
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be subdirectories "mon_L3_00" and "mon_L3_01". Each of these
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directories have one file per event (e.g. "llc_occupancy",
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"mbm_total_bytes", and "mbm_local_bytes"). In a MON group these
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files provide a read out of the current value of the event for
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all tasks in the group. In CTRL_MON groups these files provide
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the sum for all tasks in the CTRL_MON group and all tasks in
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MON groups. Please see example section for more details on usage.
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Resource allocation rules
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-------------------------
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When a task is running the following rules define which resources are
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available to it:
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1) If the task is a member of a non-default group, then the schemata
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for that group is used.
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2) Else if the task belongs to the default group, but is running on a
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CPU that is assigned to some specific group, then the schemata for the
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CPU's group is used.
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3) Otherwise the schemata for the default group is used.
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Resource monitoring rules
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-------------------------
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1) If a task is a member of a MON group, or non-default CTRL_MON group
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then RDT events for the task will be reported in that group.
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2) If a task is a member of the default CTRL_MON group, but is running
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on a CPU that is assigned to some specific group, then the RDT events
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for the task will be reported in that group.
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3) Otherwise RDT events for the task will be reported in the root level
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"mon_data" group.
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Notes on cache occupancy monitoring and control
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-----------------------------------------------
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When moving a task from one group to another you should remember that
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this only affects *new* cache allocations by the task. E.g. you may have
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a task in a monitor group showing 3 MB of cache occupancy. If you move
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to a new group and immediately check the occupancy of the old and new
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groups you will likely see that the old group is still showing 3 MB and
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the new group zero. When the task accesses locations still in cache from
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before the move, the h/w does not update any counters. On a busy system
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you will likely see the occupancy in the old group go down as cache lines
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are evicted and re-used while the occupancy in the new group rises as
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the task accesses memory and loads into the cache are counted based on
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membership in the new group.
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The same applies to cache allocation control. Moving a task to a group
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with a smaller cache partition will not evict any cache lines. The
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process may continue to use them from the old partition.
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Hardware uses CLOSid(Class of service ID) and an RMID(Resource monitoring ID)
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to identify a control group and a monitoring group respectively. Each of
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the resource groups are mapped to these IDs based on the kind of group. The
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number of CLOSid and RMID are limited by the hardware and hence the creation of
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a "CTRL_MON" directory may fail if we run out of either CLOSID or RMID
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and creation of "MON" group may fail if we run out of RMIDs.
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max_threshold_occupancy - generic concepts
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------------------------------------------
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Note that an RMID once freed may not be immediately available for use as
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the RMID is still tagged the cache lines of the previous user of RMID.
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Hence such RMIDs are placed on limbo list and checked back if the cache
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occupancy has gone down. If there is a time when system has a lot of
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limbo RMIDs but which are not ready to be used, user may see an -EBUSY
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during mkdir.
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max_threshold_occupancy is a user configurable value to determine the
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occupancy at which an RMID can be freed.
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Schemata files - general concepts
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---------------------------------
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Each line in the file describes one resource. The line starts with
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the name of the resource, followed by specific values to be applied
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in each of the instances of that resource on the system.
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Cache IDs
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---------
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On current generation systems there is one L3 cache per socket and L2
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caches are generally just shared by the hyperthreads on a core, but this
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isn't an architectural requirement. We could have multiple separate L3
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caches on a socket, multiple cores could share an L2 cache. So instead
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of using "socket" or "core" to define the set of logical cpus sharing
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a resource we use a "Cache ID". At a given cache level this will be a
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unique number across the whole system (but it isn't guaranteed to be a
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contiguous sequence, there may be gaps). To find the ID for each logical
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CPU look in /sys/devices/system/cpu/cpu*/cache/index*/id
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Cache Bit Masks (CBM)
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---------------------
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For cache resources we describe the portion of the cache that is available
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for allocation using a bitmask. The maximum value of the mask is defined
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by each cpu model (and may be different for different cache levels). It
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is found using CPUID, but is also provided in the "info" directory of
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the resctrl file system in "info/{resource}/cbm_mask". X86 hardware
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requires that these masks have all the '1' bits in a contiguous block. So
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0x3, 0x6 and 0xC are legal 4-bit masks with two bits set, but 0x5, 0x9
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and 0xA are not. On a system with a 20-bit mask each bit represents 5%
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of the capacity of the cache. You could partition the cache into four
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equal parts with masks: 0x1f, 0x3e0, 0x7c00, 0xf8000.
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Memory bandwidth(b/w) percentage
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--------------------------------
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For Memory b/w resource, user controls the resource by indicating the
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percentage of total memory b/w.
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The minimum bandwidth percentage value for each cpu model is predefined
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and can be looked up through "info/MB/min_bandwidth". The bandwidth
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granularity that is allocated is also dependent on the cpu model and can
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be looked up at "info/MB/bandwidth_gran". The available bandwidth
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control steps are: min_bw + N * bw_gran. Intermediate values are rounded
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to the next control step available on the hardware.
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The bandwidth throttling is a core specific mechanism on some of Intel
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SKUs. Using a high bandwidth and a low bandwidth setting on two threads
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sharing a core will result in both threads being throttled to use the
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low bandwidth.
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L3 schemata file details (code and data prioritization disabled)
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----------------------------------------------------------------
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With CDP disabled the L3 schemata format is:
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L3:<cache_id0>=<cbm>;<cache_id1>=<cbm>;...
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L3 schemata file details (CDP enabled via mount option to resctrl)
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------------------------------------------------------------------
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When CDP is enabled L3 control is split into two separate resources
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so you can specify independent masks for code and data like this:
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L3data:<cache_id0>=<cbm>;<cache_id1>=<cbm>;...
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L3code:<cache_id0>=<cbm>;<cache_id1>=<cbm>;...
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L2 schemata file details
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------------------------
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L2 cache does not support code and data prioritization, so the
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schemata format is always:
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L2:<cache_id0>=<cbm>;<cache_id1>=<cbm>;...
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Memory b/w Allocation details
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-----------------------------
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Memory b/w domain is L3 cache.
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MB:<cache_id0>=bandwidth0;<cache_id1>=bandwidth1;...
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Reading/writing the schemata file
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---------------------------------
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Reading the schemata file will show the state of all resources
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on all domains. When writing you only need to specify those values
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which you wish to change. E.g.
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# cat schemata
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L3DATA:0=fffff;1=fffff;2=fffff;3=fffff
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L3CODE:0=fffff;1=fffff;2=fffff;3=fffff
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# echo "L3DATA:2=3c0;" > schemata
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# cat schemata
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L3DATA:0=fffff;1=fffff;2=3c0;3=fffff
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L3CODE:0=fffff;1=fffff;2=fffff;3=fffff
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Examples for RDT allocation usage:
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Example 1
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---------
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On a two socket machine (one L3 cache per socket) with just four bits
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for cache bit masks, minimum b/w of 10% with a memory bandwidth
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granularity of 10%
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# mount -t resctrl resctrl /sys/fs/resctrl
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# cd /sys/fs/resctrl
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# mkdir p0 p1
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# echo "L3:0=3;1=c\nMB:0=50;1=50" > /sys/fs/resctrl/p0/schemata
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# echo "L3:0=3;1=3\nMB:0=50;1=50" > /sys/fs/resctrl/p1/schemata
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The default resource group is unmodified, so we have access to all parts
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of all caches (its schemata file reads "L3:0=f;1=f").
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Tasks that are under the control of group "p0" may only allocate from the
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"lower" 50% on cache ID 0, and the "upper" 50% of cache ID 1.
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Tasks in group "p1" use the "lower" 50% of cache on both sockets.
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Similarly, tasks that are under the control of group "p0" may use a
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maximum memory b/w of 50% on socket0 and 50% on socket 1.
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Tasks in group "p1" may also use 50% memory b/w on both sockets.
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Note that unlike cache masks, memory b/w cannot specify whether these
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allocations can overlap or not. The allocations specifies the maximum
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b/w that the group may be able to use and the system admin can configure
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the b/w accordingly.
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Example 2
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---------
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Again two sockets, but this time with a more realistic 20-bit mask.
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Two real time tasks pid=1234 running on processor 0 and pid=5678 running on
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processor 1 on socket 0 on a 2-socket and dual core machine. To avoid noisy
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neighbors, each of the two real-time tasks exclusively occupies one quarter
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of L3 cache on socket 0.
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# mount -t resctrl resctrl /sys/fs/resctrl
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# cd /sys/fs/resctrl
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First we reset the schemata for the default group so that the "upper"
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50% of the L3 cache on socket 0 and 50% of memory b/w cannot be used by
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ordinary tasks:
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# echo "L3:0=3ff;1=fffff\nMB:0=50;1=100" > schemata
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Next we make a resource group for our first real time task and give
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it access to the "top" 25% of the cache on socket 0.
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# mkdir p0
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# echo "L3:0=f8000;1=fffff" > p0/schemata
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Finally we move our first real time task into this resource group. We
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also use taskset(1) to ensure the task always runs on a dedicated CPU
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on socket 0. Most uses of resource groups will also constrain which
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processors tasks run on.
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# echo 1234 > p0/tasks
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# taskset -cp 1 1234
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Ditto for the second real time task (with the remaining 25% of cache):
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# mkdir p1
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# echo "L3:0=7c00;1=fffff" > p1/schemata
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# echo 5678 > p1/tasks
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# taskset -cp 2 5678
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For the same 2 socket system with memory b/w resource and CAT L3 the
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schemata would look like(Assume min_bandwidth 10 and bandwidth_gran is
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10):
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For our first real time task this would request 20% memory b/w on socket
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0.
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# echo -e "L3:0=f8000;1=fffff\nMB:0=20;1=100" > p0/schemata
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For our second real time task this would request an other 20% memory b/w
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on socket 0.
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# echo -e "L3:0=f8000;1=fffff\nMB:0=20;1=100" > p0/schemata
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Example 3
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---------
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A single socket system which has real-time tasks running on core 4-7 and
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non real-time workload assigned to core 0-3. The real-time tasks share text
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and data, so a per task association is not required and due to interaction
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with the kernel it's desired that the kernel on these cores shares L3 with
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the tasks.
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# mount -t resctrl resctrl /sys/fs/resctrl
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# cd /sys/fs/resctrl
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First we reset the schemata for the default group so that the "upper"
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50% of the L3 cache on socket 0, and 50% of memory bandwidth on socket 0
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cannot be used by ordinary tasks:
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# echo "L3:0=3ff\nMB:0=50" > schemata
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Next we make a resource group for our real time cores and give it access
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to the "top" 50% of the cache on socket 0 and 50% of memory bandwidth on
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socket 0.
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# mkdir p0
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# echo "L3:0=ffc00\nMB:0=50" > p0/schemata
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Finally we move core 4-7 over to the new group and make sure that the
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kernel and the tasks running there get 50% of the cache. They should
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also get 50% of memory bandwidth assuming that the cores 4-7 are SMT
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siblings and only the real time threads are scheduled on the cores 4-7.
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# echo F0 > p0/cpus
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4) Locking between applications
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Certain operations on the resctrl filesystem, composed of read/writes
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to/from multiple files, must be atomic.
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As an example, the allocation of an exclusive reservation of L3 cache
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involves:
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1. Read the cbmmasks from each directory
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2. Find a contiguous set of bits in the global CBM bitmask that is clear
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in any of the directory cbmmasks
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3. Create a new directory
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4. Set the bits found in step 2 to the new directory "schemata" file
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If two applications attempt to allocate space concurrently then they can
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end up allocating the same bits so the reservations are shared instead of
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exclusive.
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To coordinate atomic operations on the resctrlfs and to avoid the problem
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above, the following locking procedure is recommended:
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Locking is based on flock, which is available in libc and also as a shell
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script command
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Write lock:
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A) Take flock(LOCK_EX) on /sys/fs/resctrl
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B) Read/write the directory structure.
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C) funlock
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Read lock:
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A) Take flock(LOCK_SH) on /sys/fs/resctrl
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B) If success read the directory structure.
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C) funlock
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Example with bash:
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# Atomically read directory structure
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$ flock -s /sys/fs/resctrl/ find /sys/fs/resctrl
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# Read directory contents and create new subdirectory
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$ cat create-dir.sh
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find /sys/fs/resctrl/ > output.txt
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mask = function-of(output.txt)
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mkdir /sys/fs/resctrl/newres/
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echo mask > /sys/fs/resctrl/newres/schemata
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$ flock /sys/fs/resctrl/ ./create-dir.sh
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Example with C:
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/*
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* Example code do take advisory locks
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* before accessing resctrl filesystem
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*/
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#include <sys/file.h>
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#include <stdlib.h>
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void resctrl_take_shared_lock(int fd)
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{
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int ret;
|
|
|
|
/* take shared lock on resctrl filesystem */
|
|
ret = flock(fd, LOCK_SH);
|
|
if (ret) {
|
|
perror("flock");
|
|
exit(-1);
|
|
}
|
|
}
|
|
|
|
void resctrl_take_exclusive_lock(int fd)
|
|
{
|
|
int ret;
|
|
|
|
/* release lock on resctrl filesystem */
|
|
ret = flock(fd, LOCK_EX);
|
|
if (ret) {
|
|
perror("flock");
|
|
exit(-1);
|
|
}
|
|
}
|
|
|
|
void resctrl_release_lock(int fd)
|
|
{
|
|
int ret;
|
|
|
|
/* take shared lock on resctrl filesystem */
|
|
ret = flock(fd, LOCK_UN);
|
|
if (ret) {
|
|
perror("flock");
|
|
exit(-1);
|
|
}
|
|
}
|
|
|
|
void main(void)
|
|
{
|
|
int fd, ret;
|
|
|
|
fd = open("/sys/fs/resctrl", O_DIRECTORY);
|
|
if (fd == -1) {
|
|
perror("open");
|
|
exit(-1);
|
|
}
|
|
resctrl_take_shared_lock(fd);
|
|
/* code to read directory contents */
|
|
resctrl_release_lock(fd);
|
|
|
|
resctrl_take_exclusive_lock(fd);
|
|
/* code to read and write directory contents */
|
|
resctrl_release_lock(fd);
|
|
}
|
|
|
|
Examples for RDT Monitoring along with allocation usage:
|
|
|
|
Reading monitored data
|
|
----------------------
|
|
Reading an event file (for ex: mon_data/mon_L3_00/llc_occupancy) would
|
|
show the current snapshot of LLC occupancy of the corresponding MON
|
|
group or CTRL_MON group.
|
|
|
|
|
|
Example 1 (Monitor CTRL_MON group and subset of tasks in CTRL_MON group)
|
|
---------
|
|
On a two socket machine (one L3 cache per socket) with just four bits
|
|
for cache bit masks
|
|
|
|
# mount -t resctrl resctrl /sys/fs/resctrl
|
|
# cd /sys/fs/resctrl
|
|
# mkdir p0 p1
|
|
# echo "L3:0=3;1=c" > /sys/fs/resctrl/p0/schemata
|
|
# echo "L3:0=3;1=3" > /sys/fs/resctrl/p1/schemata
|
|
# echo 5678 > p1/tasks
|
|
# echo 5679 > p1/tasks
|
|
|
|
The default resource group is unmodified, so we have access to all parts
|
|
of all caches (its schemata file reads "L3:0=f;1=f").
|
|
|
|
Tasks that are under the control of group "p0" may only allocate from the
|
|
"lower" 50% on cache ID 0, and the "upper" 50% of cache ID 1.
|
|
Tasks in group "p1" use the "lower" 50% of cache on both sockets.
|
|
|
|
Create monitor groups and assign a subset of tasks to each monitor group.
|
|
|
|
# cd /sys/fs/resctrl/p1/mon_groups
|
|
# mkdir m11 m12
|
|
# echo 5678 > m11/tasks
|
|
# echo 5679 > m12/tasks
|
|
|
|
fetch data (data shown in bytes)
|
|
|
|
# cat m11/mon_data/mon_L3_00/llc_occupancy
|
|
16234000
|
|
# cat m11/mon_data/mon_L3_01/llc_occupancy
|
|
14789000
|
|
# cat m12/mon_data/mon_L3_00/llc_occupancy
|
|
16789000
|
|
|
|
The parent ctrl_mon group shows the aggregated data.
|
|
|
|
# cat /sys/fs/resctrl/p1/mon_data/mon_l3_00/llc_occupancy
|
|
31234000
|
|
|
|
Example 2 (Monitor a task from its creation)
|
|
---------
|
|
On a two socket machine (one L3 cache per socket)
|
|
|
|
# mount -t resctrl resctrl /sys/fs/resctrl
|
|
# cd /sys/fs/resctrl
|
|
# mkdir p0 p1
|
|
|
|
An RMID is allocated to the group once its created and hence the <cmd>
|
|
below is monitored from its creation.
|
|
|
|
# echo $$ > /sys/fs/resctrl/p1/tasks
|
|
# <cmd>
|
|
|
|
Fetch the data
|
|
|
|
# cat /sys/fs/resctrl/p1/mon_data/mon_l3_00/llc_occupancy
|
|
31789000
|
|
|
|
Example 3 (Monitor without CAT support or before creating CAT groups)
|
|
---------
|
|
|
|
Assume a system like HSW has only CQM and no CAT support. In this case
|
|
the resctrl will still mount but cannot create CTRL_MON directories.
|
|
But user can create different MON groups within the root group thereby
|
|
able to monitor all tasks including kernel threads.
|
|
|
|
This can also be used to profile jobs cache size footprint before being
|
|
able to allocate them to different allocation groups.
|
|
|
|
# mount -t resctrl resctrl /sys/fs/resctrl
|
|
# cd /sys/fs/resctrl
|
|
# mkdir mon_groups/m01
|
|
# mkdir mon_groups/m02
|
|
|
|
# echo 3478 > /sys/fs/resctrl/mon_groups/m01/tasks
|
|
# echo 2467 > /sys/fs/resctrl/mon_groups/m02/tasks
|
|
|
|
Monitor the groups separately and also get per domain data. From the
|
|
below its apparent that the tasks are mostly doing work on
|
|
domain(socket) 0.
|
|
|
|
# cat /sys/fs/resctrl/mon_groups/m01/mon_L3_00/llc_occupancy
|
|
31234000
|
|
# cat /sys/fs/resctrl/mon_groups/m01/mon_L3_01/llc_occupancy
|
|
34555
|
|
# cat /sys/fs/resctrl/mon_groups/m02/mon_L3_00/llc_occupancy
|
|
31234000
|
|
# cat /sys/fs/resctrl/mon_groups/m02/mon_L3_01/llc_occupancy
|
|
32789
|
|
|
|
|
|
Example 4 (Monitor real time tasks)
|
|
-----------------------------------
|
|
|
|
A single socket system which has real time tasks running on cores 4-7
|
|
and non real time tasks on other cpus. We want to monitor the cache
|
|
occupancy of the real time threads on these cores.
|
|
|
|
# mount -t resctrl resctrl /sys/fs/resctrl
|
|
# cd /sys/fs/resctrl
|
|
# mkdir p1
|
|
|
|
Move the cpus 4-7 over to p1
|
|
# echo f0 > p0/cpus
|
|
|
|
View the llc occupancy snapshot
|
|
|
|
# cat /sys/fs/resctrl/p1/mon_data/mon_L3_00/llc_occupancy
|
|
11234000
|
|
|