From mboxrd@z Thu Jan  1 00:00:00 1970
From: Rik van Riel <riel@redhat.com>
Subject: Re: [PATCH v2] sched/cputime: add steal clock warp handling
Date: Fri, 03 Jun 2016 09:10:07 -0400
Message-ID: <1464959407.16365.120.camel@redhat.com>
References: <1464931288-5886-1-git-send-email-wanpeng.li@hotmail.com>
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Cc: Wanpeng Li <wanpeng.li@hotmail.com>,
	Ingo Molnar <mingo@kernel.org>,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Paolo Bonzini <pbonzini@redhat.com>, Radim <rkrcmar@redhat.com>
To: Wanpeng Li <kernellwp@gmail.com>, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <1464931288-5886-1-git-send-email-wanpeng.li@hotmail.com>
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On Fri, 2016-06-03 at 13:21 +0800, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@hotmail.com>
>=20
> I observed that sometimes st is 100% instantaneous, then idle is
> 100%=C2=A0
> even if there is a cpu hog on the guest cpu after the cpu hotplug
> comes=C2=A0
> back(N.B. this can not always be readily reproduced). I add trace to=C2=
=A0
> capture it as below:
>=20
> cpuhp/1-12=C2=A0=C2=A0=C2=A0=C2=A0[001] d.h1=C2=A0=C2=A0=C2=A0167.461657:=
 account_process_tick: steal =3D
> 1291385514, prev_steal_time =3D 0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0
> cpuhp/1-12=C2=A0=C2=A0=C2=A0=C2=A0[001] d.h1=C2=A0=C2=A0=C2=A0167.461659:=
 account_process_tick:
> steal_jiffies =3D 1291=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0
> <idle>-0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0[001] d.h1=C2=A0=C2=A0=C2=A0167.462=
663: account_process_tick: steal =3D
> 18732255, prev_steal_time =3D 1291000000=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0
> <idle>-0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0[001] d.h1=C2=A0=C2=A0=C2=A0167.462=
664: account_process_tick:
> steal_jiffies =3D 18446744072437
>=20
> The steal clock warp and then steal_jiffies overflow.
>=20
> Rik also pointed out to me:
> =C2=A0
> >=20
> > I have seen stuff like that with live migration too, in the past=C2=A0
> This patch adds steal clock warp handling by a safe threshold to
> only=C2=A0
> apply steal times that are positive and smaller than one second (as=C2=A0
> long as nohz_full has the one second timer tick left), ignoring
> intervals=C2=A0
> that are negative or longer than a second, and using those to sync
> up=C2=A0
> the guest with the host.
>=20
> 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 <rkrcmar@redhat.com>
> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
>=20

Reviewed-by: Rik van Riel <riel@redhat.com>

--=20
All Rights Reversed.


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