From: Wanpeng Li <kernellwp@gmail.com>
To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: "Wanpeng Li" <wanpeng.li@hotmail.com>,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Radim Krčmář" <rkrcmar@redhat.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>,
"John Stultz" <john.stultz@linaro.org>
Subject: [PATCH v5 1/3] KVM: fix steal clock warp during guest cpu hotplug
Date: Wed, 8 Jun 2016 11:05:08 +0800 [thread overview]
Message-ID: <1465355110-21714-1-git-send-email-wanpeng.li@hotmail.com> (raw)
From: Wanpeng Li <wanpeng.li@hotmail.com>
Sometimes, after CPU hotplug you can observe a spike in stolen time
(100%) followed by the CPU being marked as 100% idle when it's actually
busy with a CPU hog task. The trace looks like the following:
cpuhp/1-12 [001] d.h1 167.461657: account_process_tick: steal = 1291385514, prev_steal_time = 0
cpuhp/1-12 [001] d.h1 167.461659: account_process_tick: steal_jiffies = 1291
<idle>-0 [001] d.h1 167.462663: account_process_tick: steal = 18732255, prev_steal_time = 1291000000
<idle>-0 [001] d.h1 167.462664: account_process_tick: steal_jiffies = 18446744072437
The sudden decrease of "steal" causes steal_jiffies to underflow.
The root cause is kvm_steal_time being reset to 0 after hot-plugging
back in a CPU. Instead, the preexisting value can be used, which is
what the core scheduler code expects.
John Stultz also reported a similar issue after guest S3.
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@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: John Stultz <john.stultz@linaro.org>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
---
v4 -> v5:
* improve commit message
v2 -> v3:
* fix the root cause
v1 -> v2:
* update patch subject, description and comments
* deal with the case where steal time suddenly increases by a ludicrous amount
arch/x86/kernel/kvm.c | 2 --
1 file changed, 2 deletions(-)
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index eea2a6f..1ef5e48 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -301,8 +301,6 @@ static void kvm_register_steal_time(void)
if (!has_steal_clock)
return;
- memset(st, 0, sizeof(*st));
-
wrmsrl(MSR_KVM_STEAL_TIME, (slow_virt_to_phys(st) | KVM_MSR_ENABLED));
pr_info("kvm-stealtime: cpu %d, msr %llx\n",
cpu, (unsigned long long) slow_virt_to_phys(st));
--
1.9.1
next 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 Wanpeng Li [this message]
2016-06-08 3:05 ` [PATCH v5 2/3] sched/cputime: Fix prev steal time accouting during cpu hotplug Wanpeng Li
2016-06-08 10:01 ` 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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