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 17:54:23 +0200
From:   Christian König <christian.koenig@....com>
To:     John Stultz <jstultz@...gle.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

Am 12.07.22 um 17:48 schrieb John Stultz:
> 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?

Because it's the desired default behavior and we shouldn't have to 
document that on every instance it is used.

IIRC it's documented centralized (but I need to dig that up as well).

What we should do instead is to have a warning on every relative timeout 
that this probably shouldn't be used as example.

Regards,+
Christian.

>
>> See here as well https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flwn.net%2FArticles%2F17744%2F&amp;data=05%7C01%7Cchristian.koenig%40amd.com%7C68a13ac3906d4ac4cc4308da641df25c%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637932377042931797%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&amp;sdata=dM4BkqnO0LrsdKBwKKMvx4zMabWrM%2FY7pPGDsdFO%2BnI%3D&amp;reserved=0 how much trouble system
>> calls with relative timeouts are.
> Yep. Well aware. :)
>
> thanks
> -john