Messages in this thread Patch in this message | | | Date | Tue, 14 Jun 2016 04:26:15 -0700 | From | tip-bot for Wanpeng Li <> | Subject | [tip:sched/core] KVM: Fix steal clock warp during guest CPU hotplug |
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Commit-ID: 2348140d58f4f4245e9635ea8f1a77e940a4d877 Gitweb: http://git.kernel.org/tip/2348140d58f4f4245e9635ea8f1a77e940a4d877 Author: Wanpeng Li <wanpeng.li@hotmail.com> AuthorDate: Mon, 13 Jun 2016 18:32:44 +0800 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Tue, 14 Jun 2016 11:13:14 +0200
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> --- arch/x86/kernel/kvm.c | 2 -- 1 file changed, 2 deletions(-)
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index eea2a6f..1ef5e48 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));
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