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
next prev parent 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 cpu hotplug 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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