1. 06 May, 2018 39 commits
  2. 05 May, 2018 1 commit
    • Anthoine Bourgeois's avatar
      KVM: x86: remove APIC Timer periodic/oneshot spikes · ecf08dad
      Anthoine Bourgeois authored
      Since the commit "8003c9ae: add APIC Timer periodic/oneshot mode VMX
      preemption timer support", a Windows 10 guest has some erratic timer
      spikes.
      
      Here the results on a 150000 times 1ms timer without any load:
      	  Before 8003c9ae | After 8003c9ae
      Max           1834us          |  86000us
      Mean          1100us          |   1021us
      Deviation       59us          |    149us
      Here the results on a 150000 times 1ms timer with a cpu-z stress test:
      	  Before 8003c9ae | After 8003c9ae
      Max          32000us          | 140000us
      Mean          1006us          |   1997us
      Deviation      140us          |  11095us
      
      The root cause of the problem is starting hrtimer with an expiry time
      already in the past can take more than 20 milliseconds to trigger the
      timer function.  It can be solved by forward such past timers
      immediately, rather than submitting them to hrtimer_start().
      In case the timer is periodic, update the target expiration and call
      hrtimer_start with it.
      
      v2: Check if the tsc deadline is already expired. Thank you Mika.
      v3: Execute the past timers immediately rather than submitting them to
      hrtimer_start().
      v4: Rearm the periodic timer with advance_periodic_target_expiration() a
      simpler version of set_target_expiration(). Thank you Paolo.
      
      Cc: Mika Penttilä <mika.penttila@nextfour.com>
      Cc: Wanpeng Li <kernellwp@gmail.com>
      Cc: Paolo Bonzini <pbonzini@redhat.com>
      Cc: stable@vger.kernel.org
      Signed-off-by: default avatarAnthoine Bourgeois <anthoine.bourgeois@blade-group.com>
      8003c9ae ("KVM: LAPIC: add APIC Timer periodic/oneshot mode VMX preemption timer support")
      Signed-off-by: default avatarRadim Krčmář <rkrcmar@redhat.com>
      ecf08dad