On 13/06/2016 12:32, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
>
> Commit e9532e69b8d1 ("sched/cputime: Fix steal time accounting vs. CPU
> hotplug") set rq->prev_* to 0 after a cpu hotplug comes back in order to
> fix the case where (after CPU hotplug) steal is smaller than
> rq->prev_steal_time.
>
> However, this should never happen. steal was only smaller because of the
> KVM-specific bug fixed by the previous patch. Worse, the previous patch
> triggers a bug on CPU hot-unplug/plug operation: because
> rq->prev_steal_time is cleared, all of the CPU's past steal time will be
> accounted again on hot-plug.
>
> Since the root cause has been fixed, we can just revert commit e9532e69b8d1.
>
> Fixes: 'commit e9532e69b8d1 ("sched/cputime: Fix steal time accounting vs. CPU hotplug")'
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
> ---
> kernel/sched/core.c | 1 -
> kernel/sched/sched.h | 13 -------------
> 2 files changed, 14 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 7f2cae4..7d45bb3 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -7213,7 +7213,6 @@ static void sched_rq_cpu_starting(unsigned int cpu)
> struct rq *rq = cpu_rq(cpu);
>
> rq->calc_load_update = calc_load_update;
> - account_reset_rq(rq);
> update_max_interval();
> }
>
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 72f1f30..de607e4 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1809,16 +1809,3 @@ static inline void cpufreq_trigger_update(u64 time) {}
> #else /* arch_scale_freq_capacity */
> #define arch_scale_freq_invariant() (false)
> #endif
> -
> -static inline void account_reset_rq(struct rq *rq)
> -{
> -#ifdef CONFIG_IRQ_TIME_ACCOUNTING
> - rq->prev_irq_time = 0;
> -#endif
> -#ifdef CONFIG_PARAVIRT
> - rq->prev_steal_time = 0;
> -#endif
> -#ifdef CONFIG_PARAVIRT_TIME_ACCOUNTING
> - rq->prev_steal_time_rq = 0;
> -#endif
> -}
>
Acked-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
