From: Boris Brezillon <boris.brezillon@collabora.com>
To: Danilo Krummrich <dakr@redhat.com>
Cc: airlied@gmail.com, daniel@ffwll.ch, matthew.brost@intel.com,
christian.koenig@amd.com, faith.ekstrand@collabora.com,
luben.tuikov@amd.com, dri-devel@lists.freedesktop.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH drm-misc-next v2] drm/sched: implement dynamic job-flow control
Date: Fri, 27 Oct 2023 09:16:40 +0200 [thread overview]
Message-ID: <20231027091640.50d68251@collabora.com> (raw)
In-Reply-To: <ZTb6azSfTV+LRGYu@pollux>
Hi Danilo,
On Tue, 24 Oct 2023 00:57:47 +0200
Danilo Krummrich <dakr@redhat.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.
> >
> > Any reason for having this special zero-means-no-update case? I mean,
> > drivers could just return sched_job->submission_credits if nothing
> > changed, and that would simplify the semantics IMHO. Another option, if
>
> I think I just did this because I thought it's a clever way to get rid of the
> need to deal with zero-sized jobs, which do not make much sense. In
> drm_sched_job_init() passing a zero job size defaults to one, which I think is
> reasonable. Doing the same thing here is more likely to hide a bug. However, the
> same is probably true for 'zero means no update' though. Maybe we should just
> WARN() in such a case.
>
> > we want to avoid the sched_job->submission_credits assignment when
> > nothing changes would be to make it a void function and let it update
> > the sched_job->submission_credits directly.
>
> Sure, that's an option as well. However, I'd probably prefer the new job size to
> be the return value. Having to sanity check job->submission_credits afterwards
> isn't that nice either.
Uh, sorry for the late reply, I see you've sent a v3 already :-/. 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
next prev parent reply other threads:[~2023-10-27 7:17 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-09 22:35 [PATCH drm-misc-next v2] drm/sched: implement dynamic job-flow control Danilo Krummrich
2023-10-10 7:41 ` Boris Brezillon
2023-10-23 22:57 ` Danilo Krummrich
2023-10-24 1:30 ` Luben Tuikov
2023-10-27 7:16 ` Boris Brezillon [this message]
2023-10-12 1:52 ` Luben Tuikov
2023-10-12 2:10 ` Danilo Krummrich
2023-10-14 1:17 ` Luben Tuikov
2023-10-23 22:35 ` Danilo Krummrich
2023-10-24 1:43 ` Luben Tuikov
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