linux-kernel - Re: [RFC][PATCH 1/3] drm: drm_syncobj: Add note in DOC about absolute timeout values

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Date:   Tue, 12 Jul 2022 08:48:07 -0700
From:   John Stultz <jstultz@...gle.com>
To:     Christian König <christian.koenig@....com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Jason Ekstrand <jason@...kstrand.net>,
        Lionel Landwerlin <lionel.g.landwerlin@...el.com>,
        Chunming Zhou <david1.zhou@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [RFC][PATCH 1/3] drm: drm_syncobj: Add note in DOC about absolute
 timeout values

On Tue, Jul 12, 2022 at 12:40 AM Christian König
<christian.koenig@....com> wrote:
> Am 12.07.22 um 06:22 schrieb John Stultz:
> > After having to debug down through the kernel to figure out
> > why my _WAIT calls were always timing out, I realized its
> > an absolute timeout value instead of the more common relative
> > timeouts.
> >
> > This detail should be called out in the documentation, as while
> > the absolute value makes sense here, its not as common for timeout
> > values.
>
> Well absolute timeout values are mandatory for making -ERESTARTSYS work
> without any additional handling.

Yes! I'm not saying it's wrong to use absolute values, just that
relative values are common enough to create some confusion here.

> So using them is recommended for ~20 years now and IIRC even documented
> somewhere.

So in addition to "somewhere", why not in the interface documentation as well?

> See here as well https://lwn.net/Articles/17744/ how much trouble system
> calls with relative timeouts are.

Yep. Well aware. :)

thanks
-john