[PATCH 1/3] [RFC]drm: add syncobj timeline support v4

[Zhou, David(ChunMing)]

> -----Original Message-----
> From: Christian König <ckoenig.leichtzumerken at gmail.com>
> Sent: Thursday, September 13, 2018 4:50 PM
> To: Zhou, David(ChunMing) <David1.Zhou at amd.com>; Koenig, Christian
> <Christian.Koenig at amd.com>; dri-devel at lists.freedesktop.org
> Cc: Dave Airlie <airlied at redhat.com>; Rakos, Daniel
> <Daniel.Rakos at amd.com>; amd-gfx at lists.freedesktop.org
> Subject: Re: [PATCH 1/3] [RFC]drm: add syncobj timeline support v4
> 
> Am 13.09.2018 um 09:43 schrieb Zhou, David(ChunMing):
> >
> >> -----Original Message-----
> >> From: Koenig, Christian
> >> Sent: Thursday, September 13, 2018 2:56 PM
> >> To: Zhou, David(ChunMing) <David1.Zhou at amd.com>; Zhou,
> >> David(ChunMing) <David1.Zhou at amd.com>; dri-
> >> devel at lists.freedesktop.org
> >> Cc: Dave Airlie <airlied at redhat.com>; Rakos, Daniel
> >> <Daniel.Rakos at amd.com>; amd-gfx at lists.freedesktop.org
> >> Subject: Re: [PATCH 1/3] [RFC]drm: add syncobj timeline support v4
> >>
> >> Am 13.09.2018 um 04:15 schrieb zhoucm1:
> >>> On 2018年09月12日 19:05, Christian König wrote:
> >>>>>>>> [SNIP]
> >>>>>>>> +static void drm_syncobj_find_signal_pt_for_wait_pt(struct
> >>>>>>>> drm_syncobj *syncobj,
> >>>>>>>> +                           struct drm_syncobj_wait_pt
> >>>>>>>> +*wait_pt) {
> >>>>>>> That whole approach still looks horrible complicated to me.
> >>>>> It's already very close to what you said before.
> >>>>>
> >>>>>>> Especially the separation of signal and wait pt is completely
> >>>>>>> unnecessary as far as I can see.
> >>>>>>> When a wait pt is requested we just need to search for the
> >>>>>>> signal point which it will trigger.
> >>>>> Yeah, I tried this, but when I implement cpu wait ioctl on
> >>>>> specific point, we need a advanced wait pt fence, otherwise, we
> >>>>> could still need old syncobj cb.
> >>>> Why? I mean you just need to call drm_syncobj_find_fence() and
> when
> >>>> that one returns NULL you use wait_event_*() to wait for a signal
> >>>> point >= your wait point to appear and try again.
> >>> e.g. when there are 3 syncobjs(A,B,C) to wait, all syncobjABC have
> >>> no fence yet, as you said, during drm_syncobj_find_fence(A) is
> >>> working on wait_event, syncobjB and syncobjC could already be
> >>> signaled, then we don't know which one is first signaled, which is
> >>> need when wait ioctl returns.
> >> I don't really see a problem with that. When you wait for the first
> >> one you need to wait for A,B,C at the same time anyway.
> >>
> >> So what you do is to register a fence callback on the fences you
> >> already have and for the syncobj which doesn't yet have a fence you
> >> make sure that they wake up your thread when they get one.
> >>
> >> So essentially exactly what drm_syncobj_fence_get_or_add_callback()
> >> already does today.
> > So do you mean we need still use old syncobj CB for that?
> 
> Yes, as far as I can see it should work.
> 
> >   Advanced wait pt is bad?
> 
> Well it isn't bad, I just don't see any advantage in it.


The advantage is to replace old syncobj cb.

> The existing mechanism
> should already be able to handle that.

I thought more a bit, we don't that mechanism at all, if use advanced wait pt, we can easily use fence array to achieve it for wait ioctl, we should use kernel existing feature as much as possible, not invent another, shouldn't we?  I remember  you said  it before.

Thanks,
David Zhou
> 
> Christian.
> 
> >
> > Thanks,
> > David Zhou
> >> Regards,
> >> Christian.
> >>
> >>> Back to my implementation, it already fixes all your concerns
> >>> before, and can be able to easily used in wait_ioctl. When you feel
> >>> that is complicated, I guess that is because we merged all logic to
> >>> that and much clean up in one patch. In fact, it already is very
> >>> simple, timeline_init/fini, create signal/wait_pt, find signal_pt
> >>> for wait_pt, garbage collection, just them.
> >>>
> >>> Thanks,
> >>> David Zhou
> >>>> Regards,
> >>>> Christian.
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