From: Eric Anholt <eric@anholt.net>
To: Paul Kocialkowski <paul.kocialkowski@bootlin.com>,
Daniel Vetter <daniel@ffwll.ch>
Cc: Daniel Stone <daniel@fooishbar.org>,
dri-devel <dri-devel@lists.freedesktop.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
Maxime Ripard <maxime.ripard@bootlin.com>,
Sean Paul <sean@poorly.run>, David Airlie <airlied@linux.ie>,
Eben Upton <eben@raspberrypi.org>,
Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Subject: Re: [PATCH v2 1/2] drm/file: Rehabilitate the firstopen hook for non-legacy drivers
Date: Fri, 29 Mar 2019 11:14:09 -0700 [thread overview]
Message-ID: <87r2appmz2.fsf@anholt.net> (raw)
In-Reply-To: <901ea65c770c80e22c69032affe3b1a22652b608.camel@bootlin.com>
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Paul Kocialkowski <paul.kocialkowski@bootlin.com> writes:
> Hi,
>
> Le vendredi 29 mars 2019 à 16:25 +0100, Daniel Vetter a écrit :
>> On Fri, Mar 29, 2019 at 04:02:23PM +0100, Paul Kocialkowski wrote:
>> > Hi,
>> >
>> > On Fri, 2019-03-29 at 09:09 +0000, Daniel Stone wrote:
>> > > Hi,
>> > >
>> > > On Thu, 28 Mar 2019 at 18:53, Daniel Vetter <daniel@ffwll.ch> wrote:
>> > > > On Thu, Mar 21, 2019 at 04:27:06PM +0100, Paul Kocialkowski wrote:
>> > > > > I don't see other options either, and using firstclose/lastopen feels
>> > > > > overall more readable in the driver code.
>> > > > >
>> > > > > I'm not sure there is such a big overhead associated with allocating
>> > > > > the binner BO (it seems that the current implementation tries to alloc
>> > > > > until the specific memory constraints for the buffer are met, so
>> > > > > perhaps that can take time). But if there is, I suppose it's best to
>> > > > > have that when starting up rather than delaying the first render
>> > > > > operation.
>> > > >
>> > > > I'm not entirely buying the "we don't need this for fbcon only" argument -
>> > > > there's plenty of dumb kms clients too (boot splash and whatever else
>> > > > there might be). If you don't want to keep this around I think allocating
>> > > > on first non-dumb bo allocation and dropping it when the last such fd
>> > > > closes sounds like a much better idea. Needs a bit more state, you need to
>> > > > track per drm_file whether you've already allocated a non-dumb bo, and a
>> > > > drm_device refcount, but that's not much. Firstopen feels like the wrong
>> > > > thing.
>> > > >
>> > > > Another option would be first_renderopen or something like that, except
>> > > > you can also render on the legacy node and I'm not sure how much there's a
>> > > > demand for this in other drivers. In the end you have open/close
>> > > > callbacks, you can do all the driver specific things you want to do in
>> > > > there.
>> > >
>> > > I'd like to avoid doing it in open where possible, since that hurts
>> > > device enumeration from userspace.
>> >
>> > I've noticed the same issue with firstopen, where our buffer is
>> > allocated/liberated a couple of times during enumeration, before the
>> > final open that stays alive during use.
>> >
>> > I'm not sure what is preferable between that and allocating when the
>> > GPU is first used. Slowing down the first GPU operation with the
>> > allocation does not sound too great either and it feels like the buffer
>> > should have been allocated earlier.
>> >
>> > To me, it feels I think it's better to have delays due to allocation at
>> > enumeration / startup rather than later on, but I might be missing some
>> > elements to have a clear idea.
>> >
>> > What do you think?
>>
>> We'll have the delay somewhere on driver load. Better to have it only once
>> (when the driver starts using gem for real), than a bunch of time, at
>> least once while enumerating and then once more while actually
>> initializing. I think if you allocat this on first non-dumb gem_create,
>> and on first command submission (just so evil userspace can't screw up the
>> hw too badly), that should be perfectly fine.
>
> I'm not totally convinced that it's okay to have a delay outside of
> init/enumeration, even if it's a smaller delay.
You'll have non-dumb buffers created during GL context creation, so
early in xserver or other KMS-and-GL-using application init anyway.
Seems like a perfectly fine plan to me.
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next prev parent reply other threads:[~2019-03-29 18:14 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-20 15:48 [PATCH v2 0/2] drm/vc4: Binner BO management improvements Paul Kocialkowski
2019-03-20 15:48 ` [PATCH v2 1/2] drm/file: Rehabilitate the firstopen hook for non-legacy drivers Paul Kocialkowski
2019-03-20 16:56 ` Eric Anholt
2019-03-21 15:27 ` Paul Kocialkowski
2019-03-21 23:12 ` Eric Anholt
2019-03-28 18:53 ` Daniel Vetter
2019-03-29 9:09 ` Daniel Stone
2019-03-29 15:02 ` Paul Kocialkowski
2019-03-29 15:25 ` Daniel Vetter
2019-03-29 15:49 ` Paul Kocialkowski
2019-03-29 18:14 ` Eric Anholt [this message]
2019-03-29 18:42 ` Daniel Stone
2019-03-29 20:21 ` Paul Kocialkowski
2019-03-29 15:07 ` Paul Kocialkowski
2019-03-20 15:48 ` [PATCH v2 2/2] drm/vc4: Allocated/liberate the binner BO at firstopen/lastclose Paul Kocialkowski
2019-03-20 16:58 ` Eric Anholt
2019-03-21 15:58 ` Paul Kocialkowski
2019-03-21 16:20 ` Eric Anholt
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