On Thu, 2010-05-27 at 17:55 +0300, Pekka Paalanen wrote:
> On Wed, 26 May 2010 23:24:57 +0200
> Maarten Maathuis <madman2...@gmail.com> wrote:
>
> > For NV04 i can understand, since it's irq driven fences, so let's
> > split the question.
> >
> > NV10+: can we reduce it to just spin_lock?
>
> I don't know the answer, but I know the theory: if there is
> any path, that can take the spinlock from an interrupt
> service path, then you must use the irq-safe version everywhere.
We could, the interrupt-based path is currently only used on really old
chips that don't have REF_CNT.
>
> > NV04: can't we rely on a normal spin lock and add it as well in
> > nv04_graph_mthd_set_ref?
>
> So if NV04 fences are driven by irqs, and the ISR needs to
> take the lock, then no, you cannot revert to irq-unsafe spinlocks.
> I'm not sure how it relates to ISR bottom halves, though.
>
> Note, that also irq-unsafe spinlocks disable preemption, which
> might be enough to disturb audio.
The spinlock was actually only ever meant to protect the list itself and
not the sequence counters.
I've attached a patch removing the spinlock use everywhere except when
we're actually going to touch the pending list, I think
last_sequence_irq is still safe as the NV04 fence IRQ handler is the
only writer.
I haven't tested beyond knowing this laptop I'm typing on still works.
Thoughts?
>
>
> my 2c
>
diff --git a/drivers/gpu/drm/nouveau/nouveau_channel.c b/drivers/gpu/drm/nouveau/nouveau_channel.c
index 1fc57ef..f9b2acf 100644
--- a/drivers/gpu/drm/nouveau/nouveau_channel.c
+++ b/drivers/gpu/drm/nouveau/nouveau_channel.c
@@ -257,9 +257,7 @@ nouveau_channel_free(struct nouveau_channel *chan)
nouveau_debugfs_channel_fini(chan);
/* Give outstanding push buffers a chance to complete */
- spin_lock_irqsave(&chan->fence.lock, flags);
nouveau_fence_update(chan);
- spin_unlock_irqrestore(&chan->fence.lock, flags);
if (chan->fence.sequence != chan->fence.sequence_ack) {
struct nouveau_fence *fence = NULL;
diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.c b/drivers/gpu/drm/nouveau/nouveau_fence.c
index faddf53..4031998 100644
--- a/drivers/gpu/drm/nouveau/nouveau_fence.c
+++ b/drivers/gpu/drm/nouveau/nouveau_fence.c
@@ -73,6 +73,7 @@ nouveau_fence_update(struct nouveau_channel *chan)
return;
chan->fence.sequence_ack = sequence;
+ spin_lock(&chan->fence.lock);
list_for_each_safe(entry, tmp, &chan->fence.pending) {
fence = list_entry(entry, struct nouveau_fence, entry);
@@ -84,6 +85,7 @@ nouveau_fence_update(struct nouveau_channel *chan)
if (sequence == chan->fence.sequence_ack)
break;
}
+ spin_unlock(&chan->fence.lock);
}
int
@@ -119,7 +121,6 @@ nouveau_fence_emit(struct nouveau_fence *fence)
{
struct drm_nouveau_private *dev_priv = fence->channel->dev->dev_private;
struct nouveau_channel *chan = fence->channel;
- unsigned long flags;
int ret;
ret = RING_SPACE(chan, 2);
@@ -127,9 +128,7 @@ nouveau_fence_emit(struct nouveau_fence *fence)
return ret;
if (unlikely(chan->fence.sequence == chan->fence.sequence_ack - 1)) {
- spin_lock_irqsave(&chan->fence.lock, flags);
nouveau_fence_update(chan);
- spin_unlock_irqrestore(&chan->fence.lock, flags);
BUG_ON(chan->fence.sequence ==
chan->fence.sequence_ack - 1);
@@ -138,9 +137,9 @@ nouveau_fence_emit(struct nouveau_fence *fence)
fence->sequence = ++chan->fence.sequence;
kref_get(&fence->refcount);
- spin_lock_irqsave(&chan->fence.lock, flags);
+ spin_lock(&chan->fence.lock);
list_add_tail(&fence->entry, &chan->fence.pending);
- spin_unlock_irqrestore(&chan->fence.lock, flags);
+ spin_unlock(&chan->fence.lock);
BEGIN_RING(chan, NvSubSw, USE_REFCNT ? 0x0050 : 0x0150, 1);
OUT_RING(chan, fence->sequence);
@@ -173,14 +172,11 @@ nouveau_fence_signalled(void *sync_obj, void *sync_arg)
{
struct nouveau_fence *fence = nouveau_fence(sync_obj);
struct nouveau_channel *chan = fence->channel;
- unsigned long flags;
if (fence->signalled)
return true;
- spin_lock_irqsave(&chan->fence.lock, flags);
nouveau_fence_update(chan);
- spin_unlock_irqrestore(&chan->fence.lock, flags);
return fence->signalled;
}
@@ -230,11 +226,10 @@ nouveau_fence_handler(struct drm_device *dev, int channel)
if (channel >= 0 && channel < dev_priv->engine.fifo.channels)
chan = dev_priv->fifos[channel];
- if (chan) {
- spin_lock_irq(&chan->fence.lock);
- nouveau_fence_update(chan);
- spin_unlock_irq(&chan->fence.lock);
- }
+ if (!chan)
+ return;
+
+ chan->fence.last_sequence_irq++;
}
int
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