linux-kernel - [tip:sched/core] sched/cputime: Fix prev steal time accouting during CPU hotplug

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Message-ID: <tip-3d89e5478bf550a50c99e93adf659369798263b0@git.kernel.org>
Date:	Tue, 14 Jun 2016 04:26:40 -0700
From:	tip-bot for Wanpeng Li <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	fweisbec@...il.com, peterz@...radead.org, riel@...hat.com,
	linux-kernel@...r.kernel.org, pbonzini@...hat.com,
	torvalds@...ux-foundation.org, hpa@...or.com, tglx@...utronix.de,
	mingo@...nel.org, wanpeng.li@...mail.com, rkrcmar@...hat.com,
	efault@....de
Subject: [tip:sched/core] sched/cputime: Fix prev steal time accouting
 during CPU hotplug

Commit-ID:  3d89e5478bf550a50c99e93adf659369798263b0
Gitweb:     http://git.kernel.org/tip/3d89e5478bf550a50c99e93adf659369798263b0
Author:     Wanpeng Li <wanpeng.li@...mail.com>
AuthorDate: Mon, 13 Jun 2016 18:32:45 +0800
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Tue, 14 Jun 2016 11:13:15 +0200

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

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@...mail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: Paolo Bonzini <pbonzini@...hat.com>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Mike Galbraith <efault@....de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Radim Krčmář <rkrcmar@...hat.com>
Cc: Rik van Riel <riel@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.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@...nel.org>
---
 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 13d0896..c1b537b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -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();
 }
 
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
-}