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198 lines
4.6 KiB
198 lines
4.6 KiB
/*
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* check TSC synchronization.
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*
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* Copyright (C) 2006, Red Hat, Inc., Ingo Molnar
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*
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* We check whether all boot CPUs have their TSC's synchronized,
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* print a warning if not and turn off the TSC clock-source.
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*
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* The warp-check is point-to-point between two CPUs, the CPU
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* initiating the bootup is the 'source CPU', the freshly booting
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* CPU is the 'target CPU'.
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*
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* Only two CPUs may participate - they can enter in any order.
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* ( The serial nature of the boot logic and the CPU hotplug lock
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* protects against more than 2 CPUs entering this code. )
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*/
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#include <linux/spinlock.h>
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#include <linux/kernel.h>
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#include <linux/init.h>
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#include <linux/smp.h>
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#include <linux/nmi.h>
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#include <asm/tsc.h>
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/*
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* Entry/exit counters that make sure that both CPUs
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* run the measurement code at once:
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*/
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static __cpuinitdata atomic_t start_count;
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static __cpuinitdata atomic_t stop_count;
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/*
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* We use a raw spinlock in this exceptional case, because
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* we want to have the fastest, inlined, non-debug version
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* of a critical section, to be able to prove TSC time-warps:
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*/
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static __cpuinitdata arch_spinlock_t sync_lock = __ARCH_SPIN_LOCK_UNLOCKED;
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static __cpuinitdata cycles_t last_tsc;
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static __cpuinitdata cycles_t max_warp;
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static __cpuinitdata int nr_warps;
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/*
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* TSC-warp measurement loop running on both CPUs:
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*/
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static __cpuinit void check_tsc_warp(void)
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{
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cycles_t start, now, prev, end;
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int i;
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rdtsc_barrier();
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start = get_cycles();
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rdtsc_barrier();
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/*
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* The measurement runs for 20 msecs:
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*/
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end = start + tsc_khz * 20ULL;
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now = start;
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for (i = 0; ; i++) {
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/*
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* We take the global lock, measure TSC, save the
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* previous TSC that was measured (possibly on
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* another CPU) and update the previous TSC timestamp.
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*/
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arch_spin_lock(&sync_lock);
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prev = last_tsc;
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rdtsc_barrier();
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now = get_cycles();
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rdtsc_barrier();
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last_tsc = now;
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arch_spin_unlock(&sync_lock);
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/*
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* Be nice every now and then (and also check whether
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* measurement is done [we also insert a 10 million
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* loops safety exit, so we dont lock up in case the
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* TSC readout is totally broken]):
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*/
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if (unlikely(!(i & 7))) {
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if (now > end || i > 10000000)
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break;
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cpu_relax();
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touch_nmi_watchdog();
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}
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/*
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* Outside the critical section we can now see whether
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* we saw a time-warp of the TSC going backwards:
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*/
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if (unlikely(prev > now)) {
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arch_spin_lock(&sync_lock);
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max_warp = max(max_warp, prev - now);
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nr_warps++;
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arch_spin_unlock(&sync_lock);
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}
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}
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WARN(!(now-start),
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"Warning: zero tsc calibration delta: %Ld [max: %Ld]\n",
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now-start, end-start);
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}
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/*
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* Source CPU calls into this - it waits for the freshly booted
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* target CPU to arrive and then starts the measurement:
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*/
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void __cpuinit check_tsc_sync_source(int cpu)
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{
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int cpus = 2;
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/*
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* No need to check if we already know that the TSC is not
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* synchronized:
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*/
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if (unsynchronized_tsc())
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return;
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if (boot_cpu_has(X86_FEATURE_TSC_RELIABLE)) {
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if (cpu == (nr_cpu_ids-1) || system_state != SYSTEM_BOOTING)
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pr_info(
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"Skipped synchronization checks as TSC is reliable.\n");
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return;
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}
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/*
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* Reset it - in case this is a second bootup:
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*/
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atomic_set(&stop_count, 0);
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/*
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* Wait for the target to arrive:
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*/
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while (atomic_read(&start_count) != cpus-1)
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cpu_relax();
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/*
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* Trigger the target to continue into the measurement too:
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*/
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atomic_inc(&start_count);
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check_tsc_warp();
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while (atomic_read(&stop_count) != cpus-1)
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cpu_relax();
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if (nr_warps) {
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pr_warning("TSC synchronization [CPU#%d -> CPU#%d]:\n",
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smp_processor_id(), cpu);
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pr_warning("Measured %Ld cycles TSC warp between CPUs, "
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"turning off TSC clock.\n", max_warp);
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mark_tsc_unstable("check_tsc_sync_source failed");
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} else {
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pr_debug("TSC synchronization [CPU#%d -> CPU#%d]: passed\n",
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smp_processor_id(), cpu);
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}
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/*
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* Reset it - just in case we boot another CPU later:
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*/
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atomic_set(&start_count, 0);
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nr_warps = 0;
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max_warp = 0;
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last_tsc = 0;
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/*
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* Let the target continue with the bootup:
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*/
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atomic_inc(&stop_count);
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}
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/*
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* Freshly booted CPUs call into this:
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*/
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void __cpuinit check_tsc_sync_target(void)
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{
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int cpus = 2;
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if (unsynchronized_tsc() || boot_cpu_has(X86_FEATURE_TSC_RELIABLE))
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return;
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/*
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* Register this CPU's participation and wait for the
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* source CPU to start the measurement:
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*/
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atomic_inc(&start_count);
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while (atomic_read(&start_count) != cpus)
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cpu_relax();
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check_tsc_warp();
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/*
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* Ok, we are done:
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*/
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atomic_inc(&stop_count);
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/*
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* Wait for the source CPU to print stuff:
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*/
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while (atomic_read(&stop_count) != cpus)
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cpu_relax();
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}
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