| From | Ben Hutchings <> | Date | Mon, 14 Nov 2016 00:14:07 +0000 | Subject | [PATCH 3.2 003/152] sched/cputime: Fix prev steal time accouting during CPU hotplug |
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3.2.84-rc1 review patch. If anyone has any objections, please let me know.
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From: Wanpeng Li <wanpeng.li@hotmail.com>
commit 3d89e5478bf550a50c99e93adf659369798263b0 upstream.
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 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 e9532e69b8d1.
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 e9532e69b8d1 ("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> [bwh: Backported to 3.2: adjust filename, context] Signed-off-by: Ben Hutchings <ben@decadent.org.uk> --- --- a/kernel/sched.c +++ b/kernel/sched.c @@ -2084,19 +2084,6 @@ EXPORT_SYMBOL_GPL(account_system_vtime); #endif /* CONFIG_IRQ_TIME_ACCOUNTING */ -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 -} - #ifdef CONFIG_PARAVIRT static inline u64 steal_ticks(u64 steal) { @@ -6869,7 +6856,6 @@ migration_call(struct notifier_block *nf case CPU_UP_PREPARE: rq->calc_load_update = calc_load_update; - account_reset_rq(rq); break; case CPU_ONLINE:
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