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

[Christian König <ckoenig.leichtzumerken@xxxxxxxxx>]

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@xxxxxxx>
>
> Tested-by: Stefan Fritsch <sf@xxxxxxxxxxx>

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.

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;