diff options
| author | Wanpeng Li <[email protected]> | 2016-06-13 18:32:44 +0800 |
|---|---|---|
| committer | Ingo Molnar <[email protected]> | 2016-06-14 11:13:14 +0200 |
| commit | 2348140d58f4f4245e9635ea8f1a77e940a4d877 (patch) | |
| tree | 40ace7992fc568e6b482a47d7d7bed6a5114ff87 | |
| parent | 07f9f22087a94e8162f77ee997c52a23f158aee8 (diff) | |
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 <[email protected]>
Signed-off-by: Wanpeng Li <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Paolo Bonzini <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: John Stultz <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Mike Galbraith <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Radim Krčmář <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
| -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)); |