Commit 3d89e547 authored Jun 13, 2016 by Wanpeng Li Committed by Ingo Molnar Jun 14, 2016

sched/cputime: Fix prev steal time accouting during CPU hotplug



Commit:

  e9532e69 ("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 time is smaller than
rq->prev_steal_time.

However, this should never happen. Steal time 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 e9532e69.

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: 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>
Fixes: 'commit e9532e69 ("sched/cputime: Fix steal time accounting vs. CPU hotplug")'
Link: http://lkml.kernel.org/r/1465813966-3116-3-git-send-email-wanpeng.li@hotmail.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 2348140d

kernel/sched/core.c

+0 −1

Original line number	Diff line number	Diff line
		@@ -7227,7 +7227,6 @@ 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();
		}

kernel/sched/sched.h

+0 −13

Original line number	Diff line number	Diff line
		@@ -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
		}

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