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

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Date:	Thu, 05 Jan 2012 12:27:32 +0530
From:	Nikunj A Dadhania <nikunj@...ux.vnet.ibm.com>
To:	Avi Kivity <avi@...hat.com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
Cc:	Rik van Riel <riel@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	peterz@...radead.org, linux-kernel@...r.kernel.org,
	bharata@...ux.vnet.ibm.com
Subject: Re: [RFC PATCH 0/4] Gang scheduling in CFS

On Wed, 04 Jan 2012 19:13:15 +0200, Avi Kivity <avi@...hat.com> wrote:
> On 01/04/2012 04:56 PM, Srivatsa Vaddagiri wrote:
> > * Avi Kivity <avi@...hat.com> [2012-01-04 16:41:58]:
> >
> > > > Here are some observation related to Baseline-only(8vm case)
> > > >
> > > >               | ple_gap=128 | ple_gap=64 | ple_gap=256 | ple_window=2048
> > > > --------------+-------------+------------+-------------+----------------
> > > > EbzyRecords/s |    2247.50  |    2132.75 |    2086.25  |      1835.62
> > > > PauseExits    | 7928154.00  | 6696342.00 | 7365999.00  |  50319582.00
> > > >
> > > > With ple_window = 2048, PauseExits is more than 6times the default case
> > > 
> > > So it looks like the default is optimal, at least wrt the cases you
> > > tested and your test workload.
> >
> > The default case still lags considerably behind the results we are seeing with
> > gang scheduling. One more interesting data point would be to see how
> > many PLE exits we are seeing when the vcpu is spinning in
> > flush_tlb_others_ipi(). Is there any easy way to determine that?
> >
> 
> You could get an exit trace (trace-cmd -e kvm:kvm_exit) and filter on
> PLE exits; the trace contains the guest %rip, so you could match it
> against flush_tlb_others_ipi().
> 
Cool, this is much easier, had to do some awk script to extract PLE
exits wrt flush_tlb_others_ipi:

Matched 9382616(86%), Not matched 1453845(14%)

So considerable ple exits are from flush_tlb_others_ipi and even then we
see:

    35.01%       ebizzy  [kernel.kallsyms]       [k] flush_tlb_others_ipi

Nikunj

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