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Date:   Fri, 27 Oct 2023 09:39:43 +0200
From:   Boris Brezillon <boris.brezillon@collabora.com>
To:     Christian =?UTF-8?B?S8O2bmln?= <christian.koenig@amd.com>
Cc:     Danilo Krummrich <dakr@redhat.com>, airlied@gmail.com,
        daniel@ffwll.ch, matthew.brost@intel.com, faith@gfxstrand.net,
        luben.tuikov@amd.com, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH drm-misc-next v3] drm/sched: implement dynamic job-flow
 control
Message-ID: <20231027093943.3f0ae992@collabora.com>
In-Reply-To: <ff389793-1226-49fd-b599-07dbda0b97be@amd.com>
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        <0bc79ae3-04fe-4e85-9fd0-e8b281148390@amd.com>
        <20231027093238.2ff8172e@collabora.com>
        <ff389793-1226-49fd-b599-07dbda0b97be@amd.com>
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On Fri, 27 Oct 2023 09:35:01 +0200
Christian K=C3=B6nig <christian.koenig@amd.com> wrote:

> Am 27.10.23 um 09:32 schrieb Boris Brezillon:
> > On Fri, 27 Oct 2023 09:22:12 +0200
> > Christian K=C3=B6nig <christian.koenig@amd.com> wrote:
> > =20
> >>> +
> >>> +	/**
> >>> +	 * @update_job_credits: Called once the scheduler is considering th=
is
> >>> +	 * job for execution.
> >>> +	 *
> >>> +	 * Drivers may use this to update the job's submission credits, whi=
ch 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 cre=
dits
> >>> +	 * 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); =20
> >> 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 =
=20
> > we need this credit-update to happen every time a job is considered for
> > execution by the scheduler. =20
>=20
> But the job is only considered for execution once. How do you see that=20
> this is called multiple times?

Nope, it's not. If drm_sched_can_queue() returns false, the scheduler
will go look for another entity that has a job ready for execution, and
get back to this entity later, and test drm_sched_can_queue() again.
Basically, any time drm_sched_can_queue() is called, the job credits
update should happen, so we have an accurate view of how many credits
this job needs.