On 13/06/2016 12:32, Wanpeng Li wrote: > From: Wanpeng Li <[email protected]> > > 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]> > Cc: Paolo Bonzini <[email protected]> > Cc: Radim Krčmář <[email protected]> > Cc: Ingo Molnar <[email protected]> > Cc: Peter Zijlstra (Intel) <[email protected]> > Cc: Rik van Riel <[email protected]> > Cc: Thomas Gleixner <[email protected]> > Cc: Frederic Weisbecker <[email protected]> > Cc: John Stultz <[email protected]> > Signed-off-by: Wanpeng Li <[email protected]> > --- > 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)); >
Because there's no cover letter, I guess I have to ack each patch independently. Acked-by: Paolo Bonzini <[email protected]> Also, there's really no relation between patches 1-2 and 3... Paolo
