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[PATCH v6 2/3] sched/cputime: Fix prev steal time accouting during cpu hotplug

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From: Wanpeng Li <wanpeng.li@hotmail.com>

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@kernel.org>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
---
 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
-}
-- 
1.9.1

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[PATCH v6 0/3] Sched, KVM: st: Add steal time support to full dynticks CPU time accounting  Wanpeng Li <kernellwp@gmail.com> - 2016-06-13 12:40 +0200
  [PATCH v6 2/3] sched/cputime: Fix prev steal time accouting during cpu hotplug Wanpeng Li <kernellwp@gmail.com> - 2016-06-13 12:40 +0200
    Re: [PATCH v6 2/3] sched/cputime: Fix prev steal time accouting  during cpu hotplug Paolo Bonzini <pbonzini@redhat.com> - 2016-06-13 12:50 +0200
    [tip:sched/core] sched/cputime: Fix prev steal time accouting  during CPU hotplug tip-bot for Wanpeng Li <tipbot@zytor.com> - 2016-06-14 13:30 +0200
  [PATCH v6 3/3] sched/cputime: Add steal time support to full dynticks CPU time accounting Wanpeng Li <kernellwp@gmail.com> - 2016-06-13 12:40 +0200
    Re: [PATCH v6 3/3] sched/cputime: Add steal time support to full  dynticks CPU time accounting Paolo Bonzini <pbonzini@redhat.com> - 2016-06-13 12:50 +0200
    [tip:sched/core] sched/cputime: Add steal time support to full  dynticks CPU time accounting tip-bot for Wanpeng Li <tipbot@zytor.com> - 2016-06-14 13:30 +0200
  Re: [PATCH v6 0/3] Sched, KVM: st: Add steal time support to full  dynticks CPU time accounting Wanpeng Li <kernellwp@gmail.com> - 2016-06-13 13:30 +0200

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