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| author | Wanpeng Li <wanpeng.li@hotmail.com> | 2016-06-13 18:32:44 +0800 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2016-06-14 11:13:14 +0200 |
| commit | 2348140d58f4f4245e9635ea8f1a77e940a4d877 (patch) | |
| tree | 40ace7992fc568e6b482a47d7d7bed6a5114ff87 /arch/x86/kernel/kvm.c | |
| parent | 07f9f22087a94e8162f77ee997c52a23f158aee8 (diff) | |
| download | linux-2348140d58f4f4245e9635ea8f1a77e940a4d877.tar.gz | |
KVM: Fix steal clock warp during guest CPU hotplug
Sometimes, after CPU hotplug you can observe a spike in stolen time (100%) followed by the CPU being marked as 100% idle when it's actually busy with a CPU hog task. The trace looks like the following: cpuhp/1-12 [001] d.h1 167.461657: account_process_tick: steal = 1291385514, prev_steal_time = 0 cpuhp/1-12 [001] d.h1 167.461659: account_process_tick: steal_jiffies = 1291 <idle>-0 [001] d.h1 167.462663: account_process_tick: steal = 18732255, prev_steal_time = 1291000000 <idle>-0 [001] d.h1 167.462664: account_process_tick: steal_jiffies = 18446744072437 The sudden decrease of "steal" causes steal_jiffies to underflow. The root cause is kvm_steal_time being reset to 0 after hot-plugging back in a CPU. Instead, the preexisting value can be used, which is what the core scheduler code expects. John Stultz also reported a similar issue after guest S3. Suggested-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Paolo Bonzini <pbonzini@redhat.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: John Stultz <john.stultz@linaro.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Radim Krčmář <rkrcmar@redhat.com> Cc: Rik van Riel <riel@redhat.com> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/1465813966-3116-2-git-send-email-wanpeng.li@hotmail.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/kernel/kvm.c')
| -rw-r--r-- | arch/x86/kernel/kvm.c | 2 |
1 files changed, 0 insertions, 2 deletions
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index eea2a6f72b31..1ef5e48b3a36 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -301,8 +301,6 @@ static void kvm_register_steal_time(void) if (!has_steal_clock) return; - memset(st, 0, sizeof(*st)); - wrmsrl(MSR_KVM_STEAL_TIME, (slow_virt_to_phys(st) | KVM_MSR_ENABLED)); pr_info("kvm-stealtime: cpu %d, msr %llx\n", cpu, (unsigned long long) slow_virt_to_phys(st)); |