Re: [Nouveau] [PATCH] drm/nouveau: wait for the exclusive fence after the shared ones v2

[Ben Skeggs <skeggsb@gmail.com>]

On Tue, 14 Dec 2021 at 19:19, Christian König
<ckoenig.leichtzumerken@gmail.com> wrote:
>
> Am 11.12.21 um 10:59 schrieb Stefan Fritsch:
> > On 09.12.21 11:23, Christian König wrote:
> >> Always waiting for the exclusive fence resulted on some performance
> >> regressions. So try to wait for the shared fences first, then the
> >> exclusive fence should always be signaled already.
> >>
> >> v2: fix incorrectly placed "(", add some comment why we do this.
> >>
> >> Signed-off-by: Christian König <christian.koenig@amd.com>
> >
> > Tested-by: Stefan Fritsch <sf@sfritsch.de>
>
> Thanks.
>
> >
> > Please also add a cc for linux-stable, so that this is fixed in 5.15.x
>
> Sure, but I still need some acked-by or rb from one of the Nouveau guys.
> So gentle ping on that.
Acked-by: Ben Skeggs <bskeggs@redhat.com>

>
> Regards,
> Christian.
>
> >
> > Cheers,
> > Stefan
> >
> >> ---
> >>   drivers/gpu/drm/nouveau/nouveau_fence.c | 28 +++++++++++++------------
> >>   1 file changed, 15 insertions(+), 13 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.c
> >> b/drivers/gpu/drm/nouveau/nouveau_fence.c
> >> index 05d0b3eb3690..0ae416aa76dc 100644
> >> --- a/drivers/gpu/drm/nouveau/nouveau_fence.c
> >> +++ b/drivers/gpu/drm/nouveau/nouveau_fence.c
> >> @@ -353,15 +353,22 @@ nouveau_fence_sync(struct nouveau_bo *nvbo,
> >> struct nouveau_channel *chan, bool e
> >>             if (ret)
> >>               return ret;
> >> -    }
> >>   -    fobj = dma_resv_shared_list(resv);
> >> -    fence = dma_resv_excl_fence(resv);
> >> +        fobj = NULL;
> >> +    } else {
> >> +        fobj = dma_resv_shared_list(resv);
> >> +    }
> >>   -    if (fence) {
> >> +    /* Waiting for the exclusive fence first causes performance
> >> regressions
> >> +     * under some circumstances. So manually wait for the shared
> >> ones first.
> >> +     */
> >> +    for (i = 0; i < (fobj ? fobj->shared_count : 0) && !ret; ++i) {
> >>           struct nouveau_channel *prev = NULL;
> >>           bool must_wait = true;
> >>   +        fence = rcu_dereference_protected(fobj->shared[i],
> >> +                        dma_resv_held(resv));
> >> +
> >>           f = nouveau_local_fence(fence, chan->drm);
> >>           if (f) {
> >>               rcu_read_lock();
> >> @@ -373,20 +380,13 @@ nouveau_fence_sync(struct nouveau_bo *nvbo,
> >> struct nouveau_channel *chan, bool e
> >>             if (must_wait)
> >>               ret = dma_fence_wait(fence, intr);
> >> -
> >> -        return ret;
> >>       }
> >>   -    if (!exclusive || !fobj)
> >> -        return ret;
> >> -
> >> -    for (i = 0; i < fobj->shared_count && !ret; ++i) {
> >> +    fence = dma_resv_excl_fence(resv);
> >> +    if (fence) {
> >>           struct nouveau_channel *prev = NULL;
> >>           bool must_wait = true;
> >>   -        fence = rcu_dereference_protected(fobj->shared[i],
> >> -                        dma_resv_held(resv));
> >> -
> >>           f = nouveau_local_fence(fence, chan->drm);
> >>           if (f) {
> >>               rcu_read_lock();
> >> @@ -398,6 +398,8 @@ nouveau_fence_sync(struct nouveau_bo *nvbo,
> >> struct nouveau_channel *chan, bool e
> >>             if (must_wait)
> >>               ret = dma_fence_wait(fence, intr);
> >> +
> >> +        return ret;
> >>       }
> >>         return ret;
>