linux-kernel - Re: [RFC PATCH 0/4] Gang scheduling in CFS

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Date:	Tue, 27 Dec 2011 16:13:26 +0530
From:	Nikunj A Dadhania <nikunj@...ux.vnet.ibm.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, peterz@...radead.org,
	linux-kernel@...r.kernel.org, vatsa@...ux.vnet.ibm.com,
	bharata@...ux.vnet.ibm.com
Subject: Re: [RFC PATCH 0/4] Gang scheduling in CFS

On Tue, 27 Dec 2011 12:34:34 +0200, Avi Kivity <avi@...hat.com> wrote:
> On 12/27/2011 12:10 PM, Nikunj A Dadhania wrote:
> > On Tue, 27 Dec 2011 11:51:46 +0200, Avi Kivity <avi@...hat.com> wrote:
> > > On 12/27/2011 11:44 AM, Nikunj A Dadhania wrote:
> > > > > > I am seeing a drop of ~44% when setting yield_on_hlt = 0
> > > > > >
> > > > > 
> > > > > A drop of 44% of what?
> > > > > 
> > > > records/sec
> > > >
> > > > Ebizzy - 2VM running in parallel, both having gang scheduling enabled.
> > > >
> > > >                     yield_on_hlt=1         yield_on_hlt=0
> > > >  EbzyRecords/sec      41955.50               23285.00            -44 
> > > >
> > > >
> > > 
> > > Interesting, are you overcommitting vcpus?
> > > 
> > Yes(1:2). On a 8cpu machine, have 2VMs running, which is 8vcpus each.
> 
> Ah, yield_on_hlt=0 isn't any good with overcommit.  The vcpu stays
> scheduled when idle, so other vcpus don't get to use its cpu time.
> 
This is similar to booting the guest with idle=poll kernel parameter?

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