linux-kernel - Re: [PATCH RFC 0/2] kvm: Improving directed yield in PLE handler

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Message-ID: <4FFD4091.8040804@redhat.com>
Date:	Wed, 11 Jul 2012 12:00:01 +0300
From:	Avi Kivity <avi@...hat.com>
To:	habanero@...ux.vnet.ibm.com
CC:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Ingo Molnar <mingo@...hat.com>, Rik van Riel <riel@...hat.com>,
	S390 <linux-s390@...r.kernel.org>,
	Carsten Otte <cotte@...ibm.com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	KVM <kvm@...r.kernel.org>, chegu vinod <chegu_vinod@...com>,
	LKML <linux-kernel@...r.kernel.org>, X86 <x86@...nel.org>,
	Gleb Natapov <gleb@...hat.com>, linux390@...ibm.com,
	Srivatsa Vaddagiri <srivatsa.vaddagiri@...il.com>,
	Joerg Roedel <joerg.roedel@....com>
Subject: Re: [PATCH RFC 0/2] kvm: Improving directed yield in PLE handler

On 07/10/2012 12:47 AM, Andrew Theurer wrote:
>          
> For the cpu threads in the host that are actually active (in this case
> 1/2 of them), ~50% of their time is in kernel and ~43% in guest.  This
> is for a no-IO workload, so that's just incredible to see so much cpu
> wasted.  I feel that 2 important areas to tackle are a more scalable
> yield_to() and reducing the number of pause exits itself (hopefully by
> just tuning ple_window for the latter).

One thing we can do is autotune ple_window.  If a ple exit fails to wake
anybody (because all vcpus are either running, sleeping, or in ple
exits) then we deduce we are not overcommitted and we can increase the
ple window.  There's the question of how to decrease it again though.

-- 
error compiling committee.c: too many arguments to function


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