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Message-ID: <3076593e-9ff1-bb73-b05c-000a7a502caa@collabora.com>
Date:   Tue, 12 Apr 2022 22:55:52 +0300
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Subject: Re: [PATCH v1] drm/scheduler: Don't kill jobs in interrupt context
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To:     Andrey Grodzovsky <andrey.grodzovsky@amd.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Tomeu Vizoso <tomeu.vizoso@collabora.com>,
        Steven Price <steven.price@arm.com>,
        Rob Herring <robh@kernel.org>,
        Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>,
        Rob Clark <robdclark@gmail.com>
Cc:     dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        Dmitry Osipenko <digetx@gmail.com>
References: <20220411221536.283312-1-dmitry.osipenko@collabora.com>
 <064d8958-a288-64e1-b2a4-c2302a456d5b@amd.com>
 <a04733af-5ff1-a1b4-527d-68b28a037231@collabora.com>
 <f6de2b9a-005f-d1f5-9818-cfbee2bdddc5@amd.com>
From:   Dmitry Osipenko <dmitry.osipenko@collabora.com>
In-Reply-To: <f6de2b9a-005f-d1f5-9818-cfbee2bdddc5@amd.com>
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On 4/12/22 22:40, Andrey Grodzovsky wrote:
> 
> On 2022-04-12 14:20, Dmitry Osipenko wrote:
>> On 4/12/22 19:51, Andrey Grodzovsky wrote:
>>> On 2022-04-11 18:15, Dmitry Osipenko wrote:
>>>> Interrupt context can't sleep. Drivers like Panfrost and MSM are taking
>>>> mutex when job is released, and thus, that code can sleep. This results
>>>> into "BUG: scheduling while atomic" if locks are contented while job is
>>>> freed. There is no good reason for releasing scheduler's jobs in IRQ
>>>> context, hence use normal context to fix the trouble.
>>>
>>> I am not sure this is the beast Idea to leave job's sw fence signalling
>>> to be
>>> executed in system_wq context which is prone to delays of executing
>>> various work items from around the system. Seems better to me to
>>> leave the
>>> fence signaling within the IRQ context and offload only the job
>>> freeing or,
>>> maybe handle rescheduling to thread context within drivers implemention
>>> of .free_job cb. Not really sure which is the better.
>> We're talking here about killing jobs when driver destroys context,
>> which doesn't feel like it needs to be a fast path. I could move the
>> signalling into drm_sched_entity_kill_jobs_cb() and use unbound wq, but
>> do we really need this for a slow path?
> 
> 
> You can't move the signaling back to drm_sched_entity_kill_jobs_cb
> since this will bring back the lockdep splat that 'drm/sched: Avoid
> lockdep spalt on killing a processes'
> was fixing.

Indeed

> I see your point and i guess we can go this way too. Another way would
> be to add to
> panfrost and msm job a  work_item and reschedule to thread context from
> within their
> .free_job callbacks but that probably to cumbersome to be justified here.

Yes, there is no clear justification for doing that.

> Andrey
> 
> 
> Reviewed-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>

Thank you!