linux-kernel - Re: [PATCH drm-misc-next v3] drm/sched: implement dynamic job-flow control

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Date:   Fri, 27 Oct 2023 09:35:01 +0200
From:   Christian König <christian.koenig@....com>
To:     Boris Brezillon <boris.brezillon@...labora.com>
Cc:     Danilo Krummrich <dakr@...hat.com>, airlied@...il.com,
        daniel@...ll.ch, matthew.brost@...el.com, faith@...strand.net,
        luben.tuikov@....com, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH drm-misc-next v3] drm/sched: implement dynamic job-flow
 control

Am 27.10.23 um 09:32 schrieb Boris Brezillon:
> On Fri, 27 Oct 2023 09:22:12 +0200
> Christian König <christian.koenig@....com> wrote:
>
>>> +
>>> +	/**
>>> +	 * @update_job_credits: Called once the scheduler is considering this
>>> +	 * job for execution.
>>> +	 *
>>> +	 * Drivers may use this to update the job's submission credits, which is
>>> +	 * useful to e.g. deduct the number of native fences which have been
>>> +	 * signaled meanwhile.
>>> +	 *
>>> +	 * The callback must either return the new number of submission credits
>>> +	 * for the given job, or zero if no update is required.
>>> +	 *
>>> +	 * This callback is optional.
>>> +	 */
>>> +	u32 (*update_job_credits)(struct drm_sched_job *sched_job);
>> Why do we need an extra callback for this?
>>
>> Just document that prepare_job() is allowed to reduce the number of
>> credits the job might need.
> ->prepare_job() is called only once if the returned fence is NULL, but
> we need this credit-update to happen every time a job is considered for
> execution by the scheduler.

But the job is only considered for execution once. How do you see that 
this is called multiple times?

Regards,
Christian.

> If you're saying this control-flow should
> be implemented with a dma_fence that's signaled when enough space is
> available, I fear Danilo's work won't be that useful to the PowerVR
> driver, unfortunately.