From: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
To: Daniel Stone <daniel@fooishbar.org>
Cc: "Christian König" <ckoenig.leichtzumerken@gmail.com>,
dri-devel <dri-devel@lists.freedesktop.org>,
"ML Mesa-dev" <mesa-dev@lists.freedesktop.org>
Subject: Re: [Mesa-dev] [RFC] Linux Graphics Next: Explicit fences everywhere and no BO fences - initial proposal
Date: Tue, 20 Apr 2021 21:03:05 +0200 [thread overview]
Message-ID: <CAP+8YyHkuABPb46a_LUtrfrsv4fvhMzjALzF+heMpSmf0UWAnQ@mail.gmail.com> (raw)
In-Reply-To: <CAPj87rN0hMHVKFzAte-mnPyPT_NUG7z=cmabTw65rJ22eQhYoQ@mail.gmail.com>
[-- Attachment #1.1: Type: text/plain, Size: 5896 bytes --]
On Tue, Apr 20, 2021 at 8:16 PM Daniel Stone <daniel@fooishbar.org> wrote:
> On Tue, 20 Apr 2021 at 19:00, Christian König <
> ckoenig.leichtzumerken@gmail.com> wrote:
>
>> Am 20.04.21 um 19:44 schrieb Daniel Stone:
>>
>> But winsys is something _completely_ different. Yes, you're using the GPU
>> to do things with buffers A, B, and C to produce buffer Z. Yes, you're
>> using vkQueuePresentKHR to schedule that work. Yes, Mutter's composition
>> job might depend on a Chromium composition job which depends on GTA's
>> render job which depends on GTA's compute job which might take a year to
>> complete. Mutter's composition job needs to complete in 'reasonable'
>> (again, FSVO) time, no matter what. The two are compatible.
>>
>> How? Don't lump them together. Isolate them aggressively, and
>> _predictably_ in a way that you can reason about.
>>
>> What clients do in their own process space is their own business. Games
>> can deadlock themselves if they get wait-before-signal wrong. Compute jobs
>> can run for a year. Their problem. Winsys is not that, because you're
>> crossing every isolation boundary possible. Process, user, container, VM -
>> every kind of privilege boundary. Thus far, dma_fence has protected us from
>> the most egregious abuses by guaranteeing bounded-time completion; it also
>> acts as a sequencing primitive, but from the perspective of a winsys person
>> that's of secondary importance, which is probably one of the bigger
>> disconnects between winsys people and GPU driver people.
>>
>>
>> Finally somebody who understands me :)
>>
>> Well the question is then how do we get winsys and your own process space
>> together then?
>>
>
> It's a jarring transition. If you take a very narrow view and say 'it's
> all GPU work in shared buffers so it should all work the same', then
> client<->winsys looks the same as client<->client gbuffer. But this is a
> trap.
>
I think this is where I think we have have a serious gap of what a winsys
or a compositor is. Like if you have only a single wayland server running
on a physical machine this is easy. But add a VR compositor, an
intermediate compositor (say gamescope), Xwayland and some containers/VM,
some video capture (or, gasp, a browser that doubles as compositor) and
this story gets seriously complicated. Like who are you protecting from
who? at what point is something client<->winsys vs. client<->client?
> Just because you can mmap() a file on an NFS server in New Zealand doesn't
> mean that you should have the same expectations of memory access to that
> file as you do to of a pointer from alloca(). Even if the primitives look
> the same, you are crossing significant boundaries, and those do not come
> without a compromise and a penalty.
>
>
>> Anyway, one of the great things about winsys (there are some! trust me)
>> is we don't need to be as hopelessly general as for game engines, nor as
>> hyperoptimised. We place strict demands on our clients, and we literally
>> kill them every single time they get something wrong in a way that's
>> visible to us. Our demands on the GPU are so embarrassingly simple that you
>> can run every modern desktop environment on GPUs which don't have unified
>> shaders. And on certain platforms who don't share tiling formats between
>> texture/render-target/scanout ... and it all still runs fast enough that
>> people don't complain.
>>
>>
>> Ignoring everything below since that is the display pipeline I'm not
>> really interested in. My concern is how to get the buffer from the client
>> to the server without allowing the client to get the server into trouble?
>>
>> My thinking is still to use timeouts to acquire texture locks. E.g. when
>> the compositor needs to access texture it grabs a lock and if that lock
>> isn't available in less than 20ms whoever is holding it is killed hard and
>> the lock given to the compositor.
>>
>> It's perfectly fine if a process has a hung queue, but if it tries to
>> send buffers which should be filled by that queue to the compositor it just
>> gets a corrupted window content.
>>
>
> Kill the client hard. If the compositor has speculatively queued sampling
> against rendering which never completed, let it access garbage. You'll have
> one frame of garbage (outdated content, all black, random pattern; the
> failure mode is equally imperfect, because there is no perfect answer),
> then the compositor will notice the client has disappeared and remove all
> its resources.
>
> It's not possible to completely prevent this situation if the compositor
> wants to speculatively pipeline work, only ameliorate it. From a
> system-global point of view, just expose the situation and let it bubble
> up. Watch the number of fences which failed to retire in time, and destroy
> the context if there are enough of them (maybe 1, maybe 100). Watch the
> number of contexts the file description get forcibly destroyed, and destroy
> the file description if there are enough of them. Watch the number of
> descriptions which get forcibly destroyed, and destroy the process if there
> are enough of them. Watch the number of processes in a cgroup/pidns which
> get forcibly destroyed, and destroy the ... etc. Whether it's the DRM
> driver or an external monitor such as systemd/Flatpak/podman/Docker doing
> that is pretty immaterial, as long as the concept of failure bubbling up
> remains.
>
> (20ms is objectively the wrong answer FWIW, because we're not a hard RTOS.
> But if our biggest point of disagreement is 20 vs. 200 vs. 2000 vs. 20000
> ms, then this thread has been a huge success!)
>
> Cheers,
> Daniel
> _______________________________________________
> mesa-dev mailing list
> mesa-dev@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/mesa-dev
>
[-- Attachment #1.2: Type: text/html, Size: 8036 bytes --]
[-- Attachment #2: Type: text/plain, Size: 160 bytes --]
_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel
next prev parent reply other threads:[~2021-04-20 19:03 UTC|newest]
Thread overview: 105+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-19 10:47 [RFC] Linux Graphics Next: Explicit fences everywhere and no BO fences - initial proposal Marek Olšák
2021-04-19 15:48 ` Jason Ekstrand
2021-04-20 2:25 ` Marek Olšák
2021-04-20 10:15 ` [Mesa-dev] " Christian König
2021-04-20 10:34 ` Daniel Vetter
2021-04-20 11:03 ` Marek Olšák
2021-04-20 11:16 ` Daniel Vetter
2021-04-20 11:59 ` Christian König
2021-04-20 14:09 ` Daniel Vetter
2021-04-20 16:24 ` Jason Ekstrand
2021-04-20 16:19 ` Jason Ekstrand
2021-04-20 12:01 ` Daniel Vetter
2021-04-20 12:19 ` [Mesa-dev] " Christian König
2021-04-20 13:03 ` Daniel Stone
2021-04-20 14:04 ` Daniel Vetter
2021-04-20 12:42 ` Daniel Stone
2021-04-20 15:45 ` Jason Ekstrand
2021-04-20 17:44 ` Daniel Stone
2021-04-20 18:00 ` [Mesa-dev] " Christian König
2021-04-20 18:15 ` Daniel Stone
2021-04-20 19:03 ` Bas Nieuwenhuizen [this message]
2021-04-20 19:18 ` Daniel Stone
2021-04-20 18:53 ` Daniel Vetter
2021-04-20 19:14 ` Daniel Stone
2021-04-20 19:29 ` Daniel Vetter
2021-04-20 20:32 ` Daniel Stone
2021-04-26 20:59 ` Marek Olšák
2021-04-27 8:02 ` Daniel Vetter
2021-04-27 11:49 ` Marek Olšák
2021-04-27 12:06 ` Christian König
2021-04-27 12:11 ` Marek Olšák
2021-04-27 12:15 ` Daniel Vetter
2021-04-27 12:27 ` Christian König
2021-04-27 12:46 ` Marek Olšák
2021-04-27 12:50 ` Christian König
2021-04-27 13:26 ` Marek Olšák
2021-04-27 15:13 ` Christian König
2021-04-27 17:31 ` Lucas Stach
2021-04-27 17:35 ` Simon Ser
2021-04-27 18:01 ` Alex Deucher
2021-04-27 18:27 ` Simon Ser
2021-04-28 10:01 ` Daniel Vetter
2021-04-28 10:05 ` Daniel Vetter
2021-04-28 10:31 ` Christian König
2021-04-28 12:21 ` Daniel Vetter
2021-04-28 12:26 ` Daniel Vetter
2021-04-28 13:11 ` Christian König
2021-04-28 13:34 ` Daniel Vetter
2021-04-28 13:37 ` Christian König
2021-04-28 14:34 ` Daniel Vetter
2021-04-28 14:45 ` Christian König
2021-04-29 11:07 ` Daniel Vetter
2021-04-28 20:39 ` Alex Deucher
2021-04-29 11:12 ` Daniel Vetter
2021-04-30 8:58 ` Daniel Vetter
2021-04-30 9:07 ` Christian König
2021-04-30 9:35 ` Daniel Vetter
2021-04-30 10:17 ` Daniel Stone
2021-04-28 12:45 ` Simon Ser
2021-04-28 13:03 ` Alex Deucher
2021-04-27 19:41 ` Jason Ekstrand
2021-04-27 21:58 ` Marek Olšák
2021-04-28 4:01 ` Jason Ekstrand
2021-04-28 5:19 ` Marek Olšák
2021-04-27 18:38 ` Dave Airlie
2021-04-27 19:23 ` Marek Olšák
2021-04-28 6:59 ` Christian König
2021-04-28 9:07 ` Michel Dänzer
2021-04-28 9:57 ` Daniel Vetter
2021-05-01 22:27 ` Marek Olšák
2021-05-03 14:42 ` Alex Deucher
2021-05-03 14:59 ` Jason Ekstrand
2021-05-03 15:03 ` Christian König
2021-05-03 15:15 ` Jason Ekstrand
2021-05-03 15:16 ` Bas Nieuwenhuizen
2021-05-03 15:23 ` Jason Ekstrand
2021-05-03 20:36 ` Marek Olšák
2021-05-04 3:11 ` Marek Olšák
2021-05-04 7:01 ` Christian König
2021-05-04 7:32 ` Daniel Vetter
2021-05-04 8:09 ` Christian König
2021-05-04 8:27 ` Daniel Vetter
2021-05-04 9:14 ` Christian König
2021-05-04 9:47 ` Daniel Vetter
2021-05-04 10:53 ` Christian König
2021-05-04 11:13 ` Daniel Vetter
2021-05-04 12:48 ` Christian König
2021-05-04 16:44 ` Daniel Vetter
2021-05-04 17:16 ` Marek Olšák
2021-05-04 21:06 ` Jason Ekstrand
2021-04-28 9:54 ` Daniel Vetter
2021-04-27 20:49 ` Jason Ekstrand
2021-04-27 12:12 ` Daniel Vetter
2021-04-20 19:16 ` Jason Ekstrand
2021-04-20 19:27 ` Daniel Vetter
2021-04-20 14:53 ` Daniel Stone
2021-04-20 14:58 ` [Mesa-dev] " Christian König
2021-04-20 15:07 ` Daniel Stone
2021-04-20 15:16 ` Christian König
2021-04-20 15:49 ` Daniel Stone
2021-04-20 16:25 ` Marek Olšák
2021-04-20 16:42 ` Jacob Lifshay
2021-04-20 18:03 ` Daniel Stone
2021-04-20 18:39 ` Daniel Vetter
2021-04-20 19:20 ` Marek Olšák
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAP+8YyHkuABPb46a_LUtrfrsv4fvhMzjALzF+heMpSmf0UWAnQ@mail.gmail.com \
--to=bas@basnieuwenhuizen.nl \
--cc=ckoenig.leichtzumerken@gmail.com \
--cc=daniel@fooishbar.org \
--cc=dri-devel@lists.freedesktop.org \
--cc=mesa-dev@lists.freedesktop.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).