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

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Message-ID: <SN6PR12MB26394D7FEE4582FD19860104F8230@SN6PR12MB2639.namprd12.prod.outlook.com>
Date:   Tue, 23 Apr 2019 17:53:02 +0000
From:   "Ghannam, Yazen" <Yazen.Ghannam@....com>
To:     "Ghannam, Yazen" <Yazen.Ghannam@....com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "len.brown@...el.com" <len.brown@...el.com>
CC:     "linux-kernel@...r.kernel.org" <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?

Thanks,
Yazen