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

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Date:   Wed, 17 Aug 2022 17:57:42 -0400
From:   matoro <matoro_mailinglist_kernel@...oro.tk>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Sergei Trofimovich <slyich@...il.com>,
        linux-kernel@...r.kernel.org, linux-ia64@...r.kernel.org
Subject: Re: [PATCH] ia64: fix clock_getre(CLOCK_MONOTONIC) to report ITC
 frequency

Hi Andrew, I came up with the prototype for this patch, but it was based 
entirely on Sergei's investigation which was documented in 
https://bugs.gentoo.org/596382.  I asked him to send it upstream because 
I'm unable to attach my realname to it due to my job.  I can place a 
signed-off-by with my handle but I understand that's normally against 
kernel policy which is why I didn't.  Either way the bulk of the work 
belongs to Sergei, I just scribbled it down, and he cleaned it up for 
this submission.

-------- Original Message --------
Subject: Re: [PATCH] ia64: fix clock_getre(CLOCK_MONOTONIC) to report 
ITC frequency
Date: 2022-08-17 15:21
 From: Andrew Morton <akpm@...ux-foundation.org>
To: Sergei Trofimovich <slyich@...il.com>

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?