linux-kernel - Re: [PATCH] ia64: fix clock_getre(CLOCK

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Date:   Sat, 20 Aug 2022 19:17:51 +0100
From:   Sergei Trofimovich <slyich@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, linux-ia64@...r.kernel.org
Subject: Re: [PATCH] ia64: fix clock_getre(CLOCK_MONOTONIC) to report ITC
 frequency

On Wed, 17 Aug 2022 12:21:03 -0700
Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Mon, 15 Aug 2022 06:49:44 +0100 Sergei Trofimovich <slyich@...il.com> wrote:
> 
> > clock_gettime(CLOCK_MONOTONIC, &tp) is very precise on ia64 as it uses
> > ITC (similar to rdtsc on x86). It's not quite a hrtimer as it is a few
> > times slower than 1ns. Usually 2-3ns.
> > 
> > clock_getres(CLOCK_MONOTONIC, &res) never reflected that fact and
> > reported 0.04s precision (1/HZ value).
> > 
> > In https://bugs.gentoo.org/596382 gstreamer's test suite failed loudly
> > when it noticed precision discrepancy.
> > 
> > Before the change:
> > 
> >     clock_getres(CLOCK_MONOTONIC, &res) reported 250Hz precision.
> > 
> > After the change:
> > 
> >     clock_getres(CLOCK_MONOTONIC, &res) reports ITC (400Mhz) precision.
> > 
> > The patch is based on matoro's fix. It adds a bit of explanation why we
> > need to special-case arch-specific clock_getres().
> >   
> 
> It would be best (and nice) to include the original developer's
> Signed-off-by: and to Cc Émeric Maschino if possible?
> 
> Could you please take care of these paperwork issues?

Sounds good!

I'll use matoro's nickname as is for S-o-B the way matoro is comfortable
with to share it. Will add Émeric in v2 and send out in a few minutes.

-- 

  Sergei