linux-kernel - Re: [PATCH RFC 0/2] kvm: Improving undercommit,overcommit scenarios in PLE handler

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Message-ID: <20121003142942.GB15253@linux.vnet.ibm.com>
Date:	Wed, 3 Oct 2012 19:59:42 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	Avi Kivity <avi@...hat.com>, Peter Zijlstra <peterz@...radead.org>
Cc:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Ingo Molnar <mingo@...hat.com>, Rik van Riel <riel@...hat.com>,
	Srikar <srikar@...ux.vnet.ibm.com>,
	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>,
	KVM <kvm@...r.kernel.org>, Jiannan Ouyang <ouyang@...pitt.edu>,
	chegu vinod <chegu_vinod@...com>,
	"Andrew M. Theurer" <habanero@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Srivatsa Vaddagiri <srivatsa.vaddagiri@...il.com>,
	Gleb Natapov <gleb@...hat.com>,
	Andrew Jones <drjones@...hat.com>
Subject: Re: [PATCH RFC 0/2] kvm: Improving undercommit,overcommit scenarios
 in PLE handler

* Avi Kivity <avi@...hat.com> [2012-09-27 14:03:59]:

> On 09/27/2012 01:23 PM, Raghavendra K T wrote:
> >>
[...]
> > 2) looking at the result (comparing A & C) , I do feel we have
> > significant in iterating over vcpus (when compared to even vmexit)
> > so We still would need undercommit fix sugested by PeterZ (improving by
> > 140%). ?
> 
> Looking only at the current runqueue?  My worry is that it misses a lot
> of cases.  Maybe try the current runqueue first and then others.
> 

Okay. Do you mean we can have something like

+       if (rq->nr_running == 1 && p_rq->nr_running == 1) {
+               yielded = -ESRCH;
+               goto out_irq;
+       }

in the Peter's patch ?

( I thought lot about && or || . Both seem to have their own cons ).
But that should be only when we have short term imbalance, as PeterZ
told.

I am experimenting all these for V2 patch. Will come back with analysis
and patch.

> Or were you referring to something else?
> 

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