On Mon, Jun 17, 2024 at 05:11:34PM +0200, Danilo Krummrich wrote:
> On 4/17/24 07:40, Dave Airlie wrote:
> > From: Dave Airlie <airl...@redhat.com>
> >
> > I'm pretty sure this optimisation is actually not a great idea,
> > and is racy with other things waiting for fences.
>
> Yes, I tried to use it in the past on scheduler tear down, to have an
> indicator whether all jobs had the chance to finish.
>
> However, it happened that using a CPU busy loop saw the fence as signaled,
> while an (event based) dma_fence was still seen as unsignaled.
If the busy loop goes through dma_fence_is_signalled this kind of stuff
shouldn't happen. But if you open-code it, it can.
-Sima
>
> >
> > Just nuke it, there should be no need to do fence waits in a
> > busy CPU loop.
> >
> > Signed-off-by: Dave Airlie <airl...@redhat.com>
>
> Applied to drm-misc-next.
>
> > ---
> > drivers/gpu/drm/nouveau/nouveau_bo.c | 2 +-
> > drivers/gpu/drm/nouveau/nouveau_chan.c | 2 +-
> > drivers/gpu/drm/nouveau/nouveau_dmem.c | 2 +-
> > drivers/gpu/drm/nouveau/nouveau_fence.c | 30 +------------------------
> > drivers/gpu/drm/nouveau/nouveau_fence.h | 2 +-
> > drivers/gpu/drm/nouveau/nouveau_gem.c | 2 +-
> > 6 files changed, 6 insertions(+), 34 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.c
> > b/drivers/gpu/drm/nouveau/nouveau_bo.c
> > index 8a30f5a0525b..a4e8f625fce6 100644
> > --- a/drivers/gpu/drm/nouveau/nouveau_bo.c
> > +++ b/drivers/gpu/drm/nouveau/nouveau_bo.c
> > @@ -902,7 +902,7 @@ nouveau_bo_move_m2mf(struct ttm_buffer_object *bo, int
> > evict,
> > * Without this the operation can timeout and we'll fallback to a
> > * software copy, which might take several minutes to finish.
> > */
> > - nouveau_fence_wait(fence, false, false);
> > + nouveau_fence_wait(fence, false);
> > ret = ttm_bo_move_accel_cleanup(bo, &fence->base, evict, false,
> > new_reg);
> > nouveau_fence_unref(&fence);
> > diff --git a/drivers/gpu/drm/nouveau/nouveau_chan.c
> > b/drivers/gpu/drm/nouveau/nouveau_chan.c
> > index 7c97b2886807..66fca95c10c7 100644
> > --- a/drivers/gpu/drm/nouveau/nouveau_chan.c
> > +++ b/drivers/gpu/drm/nouveau/nouveau_chan.c
> > @@ -72,7 +72,7 @@ nouveau_channel_idle(struct nouveau_channel *chan)
> > ret = nouveau_fence_new(&fence, chan);
> > if (!ret) {
> > - ret = nouveau_fence_wait(fence, false, false);
> > + ret = nouveau_fence_wait(fence, false);
> > nouveau_fence_unref(&fence);
> > }
> > diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c
> > b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> > index 12feecf71e75..033a09cd3c8f 100644
> > --- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
> > +++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> > @@ -128,7 +128,7 @@ static void nouveau_dmem_page_free(struct page *page)
> > static void nouveau_dmem_fence_done(struct nouveau_fence **fence)
> > {
> > if (fence) {
> > - nouveau_fence_wait(*fence, true, false);
> > + nouveau_fence_wait(*fence, false);
> > nouveau_fence_unref(fence);
> > } else {
> > /*
> > diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.c
> > b/drivers/gpu/drm/nouveau/nouveau_fence.c
> > index c3ea3cd933cd..8de941379324 100644
> > --- a/drivers/gpu/drm/nouveau/nouveau_fence.c
> > +++ b/drivers/gpu/drm/nouveau/nouveau_fence.c
> > @@ -312,39 +312,11 @@ nouveau_fence_wait_legacy(struct dma_fence *f, bool
> > intr, long wait)
> > return timeout - t;
> > }
> > -static int
> > -nouveau_fence_wait_busy(struct nouveau_fence *fence, bool intr)
> > -{
> > - int ret = 0;
> > -
> > - while (!nouveau_fence_done(fence)) {
> > - if (time_after_eq(jiffies, fence->timeout)) {
> > - ret = -EBUSY;
> > - break;
> > - }
> > -
> > - __set_current_state(intr ?
> > - TASK_INTERRUPTIBLE :
> > - TASK_UNINTERRUPTIBLE);
> > -
> > - if (intr && signal_pending(current)) {
> > - ret = -ERESTARTSYS;
> > - break;
> > - }
> > - }
> > -
> > - __set_current_state(TASK_RUNNING);
> > - return ret;
> > -}
> > -
> > int
> > -nouveau_fence_wait(struct nouveau_fence *fence, bool lazy, bool intr)
> > +nouveau_fence_wait(struct nouveau_fence *fence, bool intr)
> > {
> > long ret;
> > - if (!lazy)
> > - return nouveau_fence_wait_busy(fence, intr);
> > -
> > ret = dma_fence_wait_timeout(&fence->base, intr, 15 * HZ);
> > if (ret < 0)
> > return ret;
> > diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.h
> > b/drivers/gpu/drm/nouveau/nouveau_fence.h
> > index bc13110bdfa4..88213014b675 100644
> > --- a/drivers/gpu/drm/nouveau/nouveau_fence.h
> > +++ b/drivers/gpu/drm/nouveau/nouveau_fence.h
> > @@ -23,7 +23,7 @@ void nouveau_fence_unref(struct nouveau_fence **);
> > int nouveau_fence_emit(struct nouveau_fence *);
> > bool nouveau_fence_done(struct nouveau_fence *);
> > -int nouveau_fence_wait(struct nouveau_fence *, bool lazy, bool intr);
> > +int nouveau_fence_wait(struct nouveau_fence *, bool intr);
> > int nouveau_fence_sync(struct nouveau_bo *, struct nouveau_channel *,
> > bool exclusive, bool intr);
> > struct nouveau_fence_chan {
> > diff --git a/drivers/gpu/drm/nouveau/nouveau_gem.c
> > b/drivers/gpu/drm/nouveau/nouveau_gem.c
> > index 49c2bcbef129..f715e381da69 100644
> > --- a/drivers/gpu/drm/nouveau/nouveau_gem.c
> > +++ b/drivers/gpu/drm/nouveau/nouveau_gem.c
> > @@ -928,7 +928,7 @@ nouveau_gem_ioctl_pushbuf(struct drm_device *dev, void
> > *data,
> > }
> > if (sync) {
> > - if (!(ret = nouveau_fence_wait(fence, false, false))) {
> > + if (!(ret = nouveau_fence_wait(fence, false))) {
> > if ((ret = dma_fence_get_status(&fence->base)) == 1)
> > ret = 0;
> > }
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
