On Tue, Jan 23, 2024 at 05:25:38PM +1000, Dave Airlie wrote:
> From: Dave Airlie <airlied@xxxxxxxxxx>
>
> fences are signalled on nvidia hw using non-stall interrupts.
>
> non-stall interrupts are not latched from my reading.
>
> When nouveau emits a fence, it requests a NON_STALL signalling,
> but it only calls the interface to allow the non-stall irq to happen
> after it has already emitted the fence. A recent change
> eacabb546271 ("nouveau: push event block/allowing out of the fence context")
> made this worse by pushing out the fence allow/block to a workqueue.
>
> However I can't see how this could ever work great, since when
> enable signalling is called, the semaphore has already been emitted
> to the ring, and the hw could already have tried to set the bits,
> but it's been masked off. Changing the allowed mask later won't make
> the interrupt get called again.
>
> For now rip all of this out.
>
> This fixes a bunch of stalls seen running VK CTS sync tests.
>
> Signed-off-by: Dave Airlie <airlied@xxxxxxxxxx>
> ---
> drivers/gpu/drm/nouveau/nouveau_fence.c | 77 +++++--------------------
> drivers/gpu/drm/nouveau/nouveau_fence.h | 2 -
> 2 files changed, 16 insertions(+), 63 deletions(-)
>
> diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.c b/drivers/gpu/drm/nouveau/nouveau_fence.c
> index 5057d976fa57..d6d50cdccf75 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_fence.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_fence.c
> @@ -50,24 +50,14 @@ nouveau_fctx(struct nouveau_fence *fence)
> return container_of(fence->base.lock, struct nouveau_fence_chan, lock);
> }
>
> -static int
> +static void
> nouveau_fence_signal(struct nouveau_fence *fence)
> {
> - int drop = 0;
> -
> dma_fence_signal_locked(&fence->base);
> list_del(&fence->head);
> rcu_assign_pointer(fence->channel, NULL);
>
> - if (test_bit(DMA_FENCE_FLAG_USER_BITS, &fence->base.flags)) {
> - struct nouveau_fence_chan *fctx = nouveau_fctx(fence);
> -
> - if (atomic_dec_and_test(&fctx->notify_ref))
> - drop = 1;
> - }
> -
> dma_fence_put(&fence->base);
> - return drop;
> }
>
> static struct nouveau_fence *
> @@ -93,8 +83,7 @@ nouveau_fence_context_kill(struct nouveau_fence_chan *fctx, int error)
> if (error)
> dma_fence_set_error(&fence->base, error);
>
> - if (nouveau_fence_signal(fence))
> - nvif_event_block(&fctx->event);
> + nouveau_fence_signal(fence);
> }
> fctx->killed = 1;
> spin_unlock_irqrestore(&fctx->lock, flags);
> @@ -103,8 +92,8 @@ nouveau_fence_context_kill(struct nouveau_fence_chan *fctx, int error)
> void
> nouveau_fence_context_del(struct nouveau_fence_chan *fctx)
> {
> - cancel_work_sync(&fctx->allow_block_work);
> nouveau_fence_context_kill(fctx, 0);
> + nvif_event_block(&fctx->event);
> nvif_event_dtor(&fctx->event);
> fctx->dead = 1;
>
> @@ -127,11 +116,10 @@ nouveau_fence_context_free(struct nouveau_fence_chan *fctx)
> kref_put(&fctx->fence_ref, nouveau_fence_context_put);
> }
>
> -static int
> +static void
> nouveau_fence_update(struct nouveau_channel *chan, struct nouveau_fence_chan *fctx)
> {
> struct nouveau_fence *fence;
> - int drop = 0;
> u32 seq = fctx->read(chan);
>
> while (!list_empty(&fctx->pending)) {
> @@ -140,10 +128,8 @@ nouveau_fence_update(struct nouveau_channel *chan, struct nouveau_fence_chan *fc
> if ((int)(seq - fence->base.seqno) < 0)
> break;
>
> - drop |= nouveau_fence_signal(fence);
> + nouveau_fence_signal(fence);
> }
> -
> - return drop;
> }
>
> static int
> @@ -160,26 +146,13 @@ nouveau_fence_wait_uevent_handler(struct nvif_event *event, void *repv, u32 repc
>
> fence = list_entry(fctx->pending.next, typeof(*fence), head);
> chan = rcu_dereference_protected(fence->channel, lockdep_is_held(&fctx->lock));
> - if (nouveau_fence_update(chan, fctx))
> - ret = NVIF_EVENT_DROP;
> + nouveau_fence_update(chan, fctx);
> }
> spin_unlock_irqrestore(&fctx->lock, flags);
>
> return ret;
> }
>
> -static void
> -nouveau_fence_work_allow_block(struct work_struct *work)
> -{
> - struct nouveau_fence_chan *fctx = container_of(work, struct nouveau_fence_chan,
> - allow_block_work);
> -
> - if (atomic_read(&fctx->notify_ref) == 0)
> - nvif_event_block(&fctx->event);
> - else
> - nvif_event_allow(&fctx->event);
> -}
> -
> void
> nouveau_fence_context_new(struct nouveau_channel *chan, struct nouveau_fence_chan *fctx)
> {
> @@ -191,7 +164,6 @@ nouveau_fence_context_new(struct nouveau_channel *chan, struct nouveau_fence_cha
> } args;
> int ret;
>
> - INIT_WORK(&fctx->allow_block_work, nouveau_fence_work_allow_block);
> INIT_LIST_HEAD(&fctx->flip);
> INIT_LIST_HEAD(&fctx->pending);
> spin_lock_init(&fctx->lock);
> @@ -216,6 +188,12 @@ nouveau_fence_context_new(struct nouveau_channel *chan, struct nouveau_fence_cha
> &args.base, sizeof(args), &fctx->event);
>
> WARN_ON(ret);
> +
> + /*
> + * Always allow non-stall irq events - previously this code tried to
> + * enable/disable them, but that just seems racy as nonstall irqs are unlatched.
> + */
> + nvif_event_allow(&fctx->event);
> }
>
> int
> @@ -247,8 +225,7 @@ nouveau_fence_emit(struct nouveau_fence *fence)
> return -ENODEV;
> }
>
> - if (nouveau_fence_update(chan, fctx))
> - nvif_event_block(&fctx->event);
> + nouveau_fence_update(chan, fctx);
>
> list_add_tail(&fence->head, &fctx->pending);
> spin_unlock_irq(&fctx->lock);
> @@ -271,8 +248,8 @@ nouveau_fence_done(struct nouveau_fence *fence)
>
> spin_lock_irqsave(&fctx->lock, flags);
> chan = rcu_dereference_protected(fence->channel, lockdep_is_held(&fctx->lock));
> - if (chan && nouveau_fence_update(chan, fctx))
> - nvif_event_block(&fctx->event);
> + if (chan)
> + nouveau_fence_update(chan, fctx);
> spin_unlock_irqrestore(&fctx->lock, flags);
> }
> return dma_fence_is_signaled(&fence->base);
> @@ -530,32 +507,10 @@ static const struct dma_fence_ops nouveau_fence_ops_legacy = {
> .release = nouveau_fence_release
> };
>
> -static bool nouveau_fence_enable_signaling(struct dma_fence *f)
> -{
> - struct nouveau_fence *fence = from_fence(f);
> - struct nouveau_fence_chan *fctx = nouveau_fctx(fence);
> - bool ret;
> - bool do_work;
> -
> - if (atomic_inc_return(&fctx->notify_ref) == 0)
> - do_work = true;
> -
> - ret = nouveau_fence_no_signaling(f);
> - if (ret)
> - set_bit(DMA_FENCE_FLAG_USER_BITS, &fence->base.flags);
> - else if (atomic_dec_and_test(&fctx->notify_ref))
> - do_work = true;
> -
> - if (do_work)
> - schedule_work(&fctx->allow_block_work);
> -
> - return ret;
> -}
> -
> static const struct dma_fence_ops nouveau_fence_ops_uevent = {
> .get_driver_name = nouveau_fence_get_get_driver_name,
> .get_timeline_name = nouveau_fence_get_timeline_name,
> - .enable_signaling = nouveau_fence_enable_signaling,
> + .enable_signaling = nouveau_fence_no_signaling,
I think you can rip nouveau_fence_no_signaling out too, it doesn't do
anything more than what the signalling codepath does too.
But maybe separate path since maybe this makes an existing leak more of a
sieve, but it really should be an existing one since you cannot assume
that someone external will ever look at whether your fence is signalled or
not.
-Sima
> .signaled = nouveau_fence_is_signaled,
> .release = nouveau_fence_release
> };
> diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.h b/drivers/gpu/drm/nouveau/nouveau_fence.h
> index 28f5cf013b89..380bb0397ed2 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_fence.h
> +++ b/drivers/gpu/drm/nouveau/nouveau_fence.h
> @@ -46,8 +46,6 @@ struct nouveau_fence_chan {
> char name[32];
>
> struct nvif_event event;
> - struct work_struct allow_block_work;
> - atomic_t notify_ref;
> int dead, killed;
> };
>
> --
> 2.43.0
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
