On Thu, Dec 12, 2013 at 02:48:47PM +0200, Ville Syrjälä wrote:
> On Tue, Dec 10, 2013 at 05:02:43PM +0200, Mika Kuoppala wrote:
> > Commit 094f9a54e355 ("drm/i915: Fix __wait_seqno to use true infinite
> > timeouts") added support for __wait_seqno to detect missing interrupts and
> > go around them by polling. As there is also timeout detection in
> > __wait_seqno, the polling and timeout detection were done with the same
> > timer.
> >
> > When there has been missed interrupts and polling is needed, the timer is
> > set to trigger in (now + 1) jiffies in future, instead of the caller
> > specified timeout.
> >
> > Now when io_schedule() returns, we calculate the jiffies left to timeout
> > using the timer expiration value. As the current jiffies is now bound to be
> > always equal or greater than the expiration value, the timeout_jiffies will
> > become zero or negative and we return -ETIME to caller even tho the
> > timeout was never reached.
> >
> > Fix this by decoupling timeout calculation from timer expiration.
> >
> > v2: Commit message with some sense in it (Chris Wilson)
> >
> > v3: add parenthesis on timeout_expire calculation
> >
> > v4: don't read jiffies without timeout (Chris Wilson)
> >
> > Signed-off-by: Mika Kuoppala <mika.kuopp...@intel.com>
> > ---
> > drivers/gpu/drm/i915/i915_gem.c | 14 ++++++--------
> > 1 file changed, 6 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_gem.c
> > b/drivers/gpu/drm/i915/i915_gem.c
> > index 92149bc..6d2e786 100644
> > --- a/drivers/gpu/drm/i915/i915_gem.c
> > +++ b/drivers/gpu/drm/i915/i915_gem.c
> > @@ -1017,7 +1017,7 @@ static int __wait_seqno(struct intel_ring_buffer
> > *ring, u32 seqno,
> > drm_i915_private_t *dev_priv = ring->dev->dev_private;
> > struct timespec before, now;
> > DEFINE_WAIT(wait);
> > - long timeout_jiffies;
> > + unsigned long timeout_expire;
> > int ret;
> >
> > WARN(dev_priv->pc8.irqs_disabled, "IRQs disabled\n");
> > @@ -1025,7 +1025,7 @@ static int __wait_seqno(struct intel_ring_buffer
> > *ring, u32 seqno,
> > if (i915_seqno_passed(ring->get_seqno(ring, true), seqno))
> > return 0;
> >
> > - timeout_jiffies = timeout ? timespec_to_jiffies_timeout(timeout) : 1;
> > + timeout_expire = timeout ? jiffies +
> > timespec_to_jiffies_timeout(timeout) : 0;
> >
> > if (dev_priv->info->gen >= 6 && can_wait_boost(file_priv)) {
> > gen6_rps_boost(dev_priv);
> > @@ -1044,7 +1044,6 @@ static int __wait_seqno(struct intel_ring_buffer
> > *ring, u32 seqno,
> > getrawmonotonic(&before);
> > for (;;) {
> > struct timer_list timer;
> > - unsigned long expire;
> >
> > prepare_to_wait(&ring->irq_queue, &wait,
> > interruptible ? TASK_INTERRUPTIBLE :
> > TASK_UNINTERRUPTIBLE);
> > @@ -1070,23 +1069,22 @@ static int __wait_seqno(struct intel_ring_buffer
> > *ring, u32 seqno,
> > break;
> > }
> >
> > - if (timeout_jiffies <= 0) {
> > + if (timeout && time_after_eq(jiffies, timeout_expire)) {
> > ret = -ETIME;
> > break;
> > }
> >
> > timer.function = NULL;
> > if (timeout || missed_irq(dev_priv, ring)) {
> > + unsigned long expire;
> > +
> > setup_timer_on_stack(&timer, fake_irq, (unsigned
> > long)current);
> > - expire = jiffies + (missed_irq(dev_priv, ring) ? 1:
> > timeout_jiffies);
> > + expire = missed_irq(dev_priv, ring) ? jiffies + 1 :
> > timeout_expire;
>
> I guess we have very small race here if we get called w/ timeout==NULL, and
> missed_irq() was true above but is no longer true here. At that point we would
> set expire=0 and might end up waiting for quite a while. But that issue was
> present already in the code before this patch and otherwise it all
> looks good to me, so:
We shouldn't ever reset misseq_irq in normal operations, so this should be
ok.
> Reviewed-by: Ville Syrjälä <ville.syrj...@linux.intel.com>
Queued for -next, thanks for the patch.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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