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From: Wanpeng Li <kernellwp@gmail.com>
To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: "Wanpeng Li" <wanpeng.li@hotmail.com>,
	"Ingo Molnar" <mingo@kernel.org>,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>,
	"Rik van Riel" <riel@redhat.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Frederic Weisbecker" <fweisbec@gmail.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>
Subject: [PATCH v5 2/3] sched/cputime: Fix prev steal time accouting during cpu hotplug
Date: Wed,  8 Jun 2016 11:05:09 +0800	[thread overview]
Message-ID: <1465355110-21714-2-git-send-email-wanpeng.li@hotmail.com> (raw)
In-Reply-To: <1465355110-21714-1-git-send-email-wanpeng.li@hotmail.com>

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 scenario:

| steal is smaller than rq->prev_steal_time we end up with an insane large
| value which then gets added to rq->prev_steal_time, resulting in a permanent
| wreckage of the accounting.

However, it is still buggy.

rq->prev_steal_time = 0:

As Rik pointed out:

| setting rq->prev_irq_time to 0 in the guest, and then getting a giant value from 
| the host, could result in a very large of steal_jiffies.

rq->prev_steal_time_rq = 0:

| steal = paravirt_steal_clock(cpu_of(rq));
| steal -= rq->prev_steal_time_rq;
|
| if (unlikely(steal > delta))
|	 steal = delta;
|
| rq->prev_steal_time_rq += steal;
| delta -= steal;
|
| rq->clock_task += delta;

steal is a giant value and rq->prev_steal_time_rq is 0, rq->prev_steal_time_rq 
grows in delta granularity, rq->clock_task can't ramp up until rq->prev_steal_time_rq 
catches up steal clock since delta value will be 0 after reducing steal time from 
normal execution time. That's why I obersved that cpuhg/1-12 continue running 
until rq->prev_steal_time_rq catches up steal clock timestamp.

I believe rq->prev_irq_time has similar issue. So this patch fix it by reverting  
commit e9532e69b8d1.

Fixes: 'commit e9532e69b8d1 ("sched/cputime: Fix steal time accounting vs. CPU hotplug")'
Acked-by: Rik van Riel <riel@redhat.com>
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>
---
v4 -> v5:
 * revert commit e9532e69b8d1 

 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

  reply	other threads:[~2016-06-08  3:05 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-08  3:05 [PATCH v5 1/3] KVM: fix steal clock warp during guest " Wanpeng Li
2016-06-08  3:05 ` Wanpeng Li [this message]
2016-06-08 10:01   ` [PATCH v5 2/3] sched/cputime: Fix prev steal time accouting during " Paolo Bonzini
2016-06-08 10:59     ` Wanpeng Li
2016-06-08  3:05 ` [PATCH v5 3/3] sched/cputime: Add steal time support to full dynticks CPU time accounting Wanpeng Li
2016-06-08  7:22   ` Ingo Molnar
2016-06-08  7:27     ` Wanpeng Li
2016-06-08  7:52       ` Ingo Molnar
2016-06-08  8:04         ` Wanpeng Li
2016-06-08  8:12           ` Wanpeng Li
2016-06-08 10:14   ` Paolo Bonzini
2016-06-08 11:11     ` Wanpeng Li
2016-06-13  3:38     ` Wanpeng Li
2016-06-13  7:55       ` Paolo Bonzini
2016-06-13  8:09         ` Wanpeng Li
2016-06-08 19:05   ` Rik van Riel
2016-06-08 23:57     ` Wanpeng Li
2016-06-09  1:20       ` Rik van Riel

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