linux-kernel - Re: [PATCH] tools/power turbostat: Make interval calculation per thread to reduce jitter

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Message-ID: <CAJvTdKk28qQnVv-fMkd6dPGrbfYryp+7PRHgqyurLyavMHSGbw@mail.gmail.com>
Date:   Sat, 31 Aug 2019 12:48:32 -0400
From:   Len Brown <lenb@...nel.org>
To:     "Ghannam, Yazen" <Yazen.Ghannam@....com>
Cc:     "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "len.brown@...el.com" <len.brown@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tools/power turbostat: Make interval calculation per
 thread to reduce jitter

Yeah, I like this patch, and I have applied it.

thanks!
-Len

On Fri, Jun 7, 2019 at 12:28 PM Ghannam, Yazen <Yazen.Ghannam@....com> wrote:
>
> > -----Original Message-----
> > From: Ghannam, Yazen <Yazen.Ghannam@....com>
> > Sent: Tuesday, April 23, 2019 12:53 PM
> > To: Ghannam, Yazen <Yazen.Ghannam@....com>; linux-pm@...r.kernel.org; len.brown@...el.com
> > Cc: linux-kernel@...r.kernel.org; Len Brown <lenb@...nel.org>
> > Subject: RE: [PATCH] tools/power turbostat: Make interval calculation per thread to reduce jitter
> >
> > > -----Original Message-----
> > > From: linux-kernel-owner@...r.kernel.org <linux-kernel-owner@...r.kernel.org> On Behalf Of Ghannam, Yazen
> > > Sent: Monday, March 25, 2019 12:33 PM
> > > To: linux-pm@...r.kernel.org
> > > Cc: Ghannam, Yazen <Yazen.Ghannam@....com>; linux-kernel@...r.kernel.org; lenb@...nel.org
> > > Subject: [PATCH] tools/power turbostat: Make interval calculation per thread to reduce jitter
> > >
> > > From: Yazen Ghannam <yazen.ghannam@....com>
> > >
> > > Turbostat currently normalizes TSC and other values by dividing by an
> > > interval. This interval is the delta between the start of one global
> > > (all counters on all CPUs) sampling and the start of another. However,
> > > this introduces a lot of jitter into the data.
> > >
> > > In order to reduce jitter, the interval calculation should be based on
> > > timestamps taken per thread and close to the start of the thread's
> > > sampling.
> > >
> > > Define a per thread time value to hold the delta between samples taken
> > > on the thread.
> > >
> > > Use the timestamp taken at the beginning of sampling to calculate the
> > > delta.
> > >
> > > Move the thread's beginning timestamp to after the CPU migration to
> > > avoid jitter due to the migration.
> > >
> > > Use the global time delta for the average time delta.
> > >
> > > Signed-off-by: Yazen Ghannam <yazen.ghannam@....com>
> > > ---
> >
> > Hi Len,
> >
> > Any comments on this patch?
> >
>
> Hi Len,
>
> Just wanted to check in. Do you have any comments on this patch?
>
> Thanks,
> Yazen



-- 
Len Brown, Intel Open Source Technology Center