x86/smpboot: Speed up suspend/resume by avoiding 100ms sleep for CPU offline during S3
With certain kernel configurations, CPU offline consumes more than 100ms during S3. It's a timing related issue: native_cpu_die() would occasionally fall into a 100ms sleep when the CPU idle loop thread marked the CPU state to DEAD too slowly. What native_cpu_die() does is that it polls the CPU state and waits for 100ms if CPU state hasn't been marked to DEAD. The 100ms sleep doesn't make sense and is purely historic. To avoid such long sleeping, this patch adds a 'struct completion' to each CPU, waits for the completion in native_cpu_die() and wakes up the completion when the CPU state is marked to DEAD. Tested on an Intel Xeon server with 48 cores, Ivybridge and on Haswell laptops. The CPU offlining cost on these machines is reduced from more than 100ms to less than 5ms. The system suspend time is reduced by 2.3s on the servers. Borislav and Prarit also helped to test the patch on an AMD machine and a few systems of various sizes and configurations (multi-socket, single-socket, no hyper threading, etc.). No issues were seen. Tested-by: Prarit Bhargava <prarit@redhat.com> Signed-off-by: Lan Tianyu <tianyu.lan@intel.com> Acked-by: Borislav Petkov <bp@suse.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: srostedt@redhat.com Cc: toshi.kani@hp.com Cc: imammedo@redhat.com Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/1409039025-32310-1-git-send-email-tianyu.lan@intel.com [ Improved a few minor details in the code, cleaned up the changelog. ] Signed-off-by: Ingo Molnar <mingo@kernel.org>
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@ -102,6 +102,8 @@ DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_llc_shared_map);
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DEFINE_PER_CPU_SHARED_ALIGNED(struct cpuinfo_x86, cpu_info);
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EXPORT_PER_CPU_SYMBOL(cpu_info);
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static DEFINE_PER_CPU(struct completion, die_complete);
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atomic_t init_deasserted;
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/*
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@ -1323,27 +1325,25 @@ int native_cpu_disable(void)
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return ret;
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clear_local_APIC();
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init_completion(&per_cpu(die_complete, smp_processor_id()));
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cpu_disable_common();
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return 0;
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}
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void native_cpu_die(unsigned int cpu)
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{
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/* We don't do anything here: idle task is faking death itself. */
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unsigned int i;
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wait_for_completion_timeout(&per_cpu(die_complete, cpu), HZ);
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for (i = 0; i < 10; i++) {
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/* They ack this in play_dead by setting CPU_DEAD */
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/* They ack this in play_dead() by setting CPU_DEAD */
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if (per_cpu(cpu_state, cpu) == CPU_DEAD) {
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if (system_state == SYSTEM_RUNNING)
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pr_info("CPU %u is now offline\n", cpu);
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return;
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}
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msleep(100);
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}
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} else {
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pr_err("CPU %u didn't die...\n", cpu);
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}
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}
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void play_dead_common(void)
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{
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@ -1354,6 +1354,7 @@ void play_dead_common(void)
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mb();
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/* Ack it */
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__this_cpu_write(cpu_state, CPU_DEAD);
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complete(&per_cpu(die_complete, smp_processor_id()));
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/*
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* With physical CPU hotplug, we should halt the cpu
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