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

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Message-ID: <20231027091755.3635be36@collabora.com>
Date:   Fri, 27 Oct 2023 09:17:55 +0200
From:   Boris Brezillon <boris.brezillon@...labora.com>
To:     Danilo Krummrich <dakr@...hat.com>
Cc:     airlied@...il.com, daniel@...ll.ch, matthew.brost@...el.com,
        christian.koenig@....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

Hi Danilo,

On Thu, 26 Oct 2023 18:13:00 +0200
Danilo Krummrich <dakr@...hat.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);

I'm copying my late reply to v2 here so it doesn't get lost:

I keep thinking it'd be simpler to make this a void function that
updates s_job->submission_credits directly. I also don't see the
problem with doing a sanity check on job->submission_credits. I mean,
if the driver is doing something silly, you can't do much to prevent it
anyway, except warn the user that something wrong has happened. If you
want to

	WARN_ON(job->submission_credits == 0 ||
		job->submission_credits > job_old_submission_credits);

that's fine. But none of this sanity checking has to do with the
function prototype/semantics, and I'm still not comfortable with this 0
=> no-change. If there's no change, we should just leave  
job->submission_credits unchanged (or return job->submission_credits)
instead of inventing a new special case.

Regards,

Boris