linux-kernel - Re: [PATCH v2 2/6] drm/sched: Prevent teardown waitque from blocking too long

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Message-ID: <e152d20b-c62e-47d9-a891-7910d1d24c6a@igalia.com>
Date: Fri, 16 May 2025 11:19:50 +0100
From: Tvrtko Ursulin <tvrtko.ursulin@...lia.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: Philipp Stanner <phasta@...nel.org>, Lyude Paul <lyude@...hat.com>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Matthew Brost <matthew.brost@...el.com>,
 Christian König <ckoenig.leichtzumerken@...il.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 dri-devel@...ts.freedesktop.org, nouveau@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org, Danilo Krummrich <dakr@...hat.com>
Subject: Re: [PATCH v2 2/6] drm/sched: Prevent teardown waitque from blocking
 too long


On 16/05/2025 10:53, Danilo Krummrich wrote:
> On Fri, May 16, 2025 at 10:33:30AM +0100, Tvrtko Ursulin wrote:
>> On 24/04/2025 10:55, Philipp Stanner wrote:
>>> +	 * @kill_fence_context: kill the fence context belonging to this scheduler
>>
>> Which fence context would that be? ;)
> 
> There's one one per ring and a scheduler instance represents a single ring. So,
> what should be specified here?

I was pointing out the fact not all drivers are 1:1 sched:entity. So 
plural at least. Thought it would be obvious from the ";)".

>> Also, "fence context" would be a new terminology in gpu_scheduler.h API
>> level. You could call it ->sched_fini() or similar to signify at which point
>> in the API it gets called and then the fact it takes sched as parameter
>> would be natural.
> 
> The driver should tear down the fence context in this callback, not the while
> scheduler. ->sched_fini() would hence be misleading.

Not the while what? Not while drm_sched_fini()? Could call it 
sched_kill() or anything. My point is that we dont' have "fence context" 
in the API but entities so adding a new term sounds sub-optimal.

>> We also probably want some commentary on the topic of indefinite (or very
>> long at least) blocking a thread exit / SIGINT/TERM/KILL time.
> 
> You mean in case the driver does implement the callback, but does *not* properly
> tear down the fence context? So, you ask for describing potential consequences
> of drivers having bugs in the implementation of the callback? Or something else?

I was proposing the kerneldoc for the vfunc should document the callback 
must not block, or if blocking is unavoidable, either document a 
guideline on how long is acceptable. Maybe even enforce a limit in the 
scheduler core itself.

Regards,

Tvrtko