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

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Date:	Tue, 27 Dec 2011 15:14:20 +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 11:17:29 +0200, Avi Kivity <avi@...hat.com> wrote:
> On 12/27/2011 05:15 AM, Nikunj A Dadhania wrote:
> > On Mon, 26 Dec 2011 08:44:58 +0530, Nikunj A Dadhania <nikunj@...ux.vnet.ibm.com> wrote:
> > > On Sun, 25 Dec 2011 12:58:15 +0200, Avi Kivity <avi@...hat.com> wrote:
> > > > On 12/23/2011 12:36 PM, Ingo Molnar wrote:
> > > > > * Nikunj A Dadhania <nikunj@...ux.vnet.ibm.com> wrote:
> > > > >
> > > [...]
> > > > > > 
> > > > > > I see the main difference between both the reports is:
> > > > > > native_flush_tlb_others.
> > > > >
> > > > > So it would be important to figure out why ebizzy gets into so 
> > > > > many TLB flushes and why gang scheduling makes it go away.
> > > > 
> > > > The second part is easy - a remote tlb flush involves IPIs to many other
> > > > vcpus (possible waking them up and scheduling them), then busy-waiting
> > > > until they acknowledge the flush.  Gang scheduling is really good here
> > > > since it shortens the busy wait, would be even better if we schedule
> > > > halted vcpus (see the yield_on_hlt module parameter, set to 0). 
> > > I will check this.
> > > 
> > 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 

Nikunj

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