Re: [Intel-gfx] [PATCH] drm/i915: Break i915_spin_request() if we see an interrupt

[Chris Wilson]

On Thu, Feb 16, 2017 at 01:26:58PM +, Tvrtko Ursulin wrote:
> 
> 
> On 16/02/2017 13:17, Mika Kuoppala wrote:
> >Chris Wilson  writes:
> >
> >>If an interrupt has been posted, and we were spinning on the active
> >>seqno waiting for it to advance but it did not, then we can expect that
> >>it will not see its advance in the immediate future
> >
> >Why we can expect this?
> 
> Maybe it should be "if (engine->irq_seqno_barrier && test_bit(...))"
> if my thinking is right that this expectation applies on platforms
> with slow barriers?

True, those others don't do the clear. And even where we have the
barrier, we only sometimes clear the bit (we interpret the bit to really
mean whether or not we have applied the barrier).

That leaves me with:

unsinged int irq_count = atomic_read(>engine->irq_count);

...

if (atomic_read(>engine->irq_count) != irq_count))
break;

Based on the new breadcrumbs hang/waitcheck.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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Re: [Intel-gfx] [PATCH] drm/i915: Break i915_spin_request() if we see an interrupt

[Tvrtko Ursulin]

On 16/02/2017 13:17, Mika Kuoppala wrote:

Chris Wilson  writes:


If an interrupt has been posted, and we were spinning on the active
seqno waiting for it to advance but it did not, then we can expect that
it will not see its advance in the immediate future


Why we can expect this?


Maybe it should be "if (engine->irq_seqno_barrier && test_bit(...))" if 
my thinking is right that this expectation applies on platforms with 
slow barriers?


Regards,

Tvrtko




and should call into
the irq-seqno barrier. We can stop spinning at this point, and leave the
difficulty of handling the coherency to the caller.

Signed-off-by: Chris Wilson 
Cc: Tvrtko Ursulin 
---
 drivers/gpu/drm/i915/i915_gem_request.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gem_request.c 
b/drivers/gpu/drm/i915/i915_gem_request.c
index 7760d7481f85..9e42b2687cae 100644
--- a/drivers/gpu/drm/i915/i915_gem_request.c
+++ b/drivers/gpu/drm/i915/i915_gem_request.c
@@ -993,6 +993,9 @@ bool __i915_spin_request(const struct drm_i915_gem_request 
*req,
  seqno))
return true;

+   if (test_bit(ENGINE_IRQ_BREADCRUMB, >engine->irq_posted))
+   break;
+
if (signal_pending_state(state, current))
break;

--
2.11.0

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Re: [Intel-gfx] [PATCH] drm/i915: Break i915_spin_request() if we see an interrupt

[Chris Wilson]

On Thu, Feb 16, 2017 at 03:17:30PM +0200, Mika Kuoppala wrote:
> Chris Wilson  writes:
> 
> > If an interrupt has been posted, and we were spinning on the active
> > seqno waiting for it to advance but it did not, then we can expect that
> > it will not see its advance in the immediate future
> 
> Why we can expect this?

The seqno is meant to arrive *before* the interrupt. The check is lazy,
but assume it is

irq_posted = test_bit(ENGINE_IRQ_BREADCRUMB, >engine->irq_posted);
if (seqno_passed())
return true;
if (irq_posted)
return false;

with the strong read ordering imposed. The reason why I think we can be
lax is that we expect the caller to check after spin_request reports
false (just it may do some other work in the meantime).

Note that the interrupt will only be detected if there is already a
waiter (or equivalent).
-Chris

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Re: [Intel-gfx] [PATCH] drm/i915: Break i915_spin_request() if we see an interrupt

[Mika Kuoppala]

Chris Wilson  writes:

> If an interrupt has been posted, and we were spinning on the active
> seqno waiting for it to advance but it did not, then we can expect that
> it will not see its advance in the immediate future

Why we can expect this?
-Mika

> and should call into
> the irq-seqno barrier. We can stop spinning at this point, and leave the
> difficulty of handling the coherency to the caller.
>
> Signed-off-by: Chris Wilson 
> Cc: Tvrtko Ursulin 
> ---
>  drivers/gpu/drm/i915/i915_gem_request.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem_request.c 
> b/drivers/gpu/drm/i915/i915_gem_request.c
> index 7760d7481f85..9e42b2687cae 100644
> --- a/drivers/gpu/drm/i915/i915_gem_request.c
> +++ b/drivers/gpu/drm/i915/i915_gem_request.c
> @@ -993,6 +993,9 @@ bool __i915_spin_request(const struct 
> drm_i915_gem_request *req,
> seqno))
>   return true;
>  
> + if (test_bit(ENGINE_IRQ_BREADCRUMB, >engine->irq_posted))
> + break;
> +
>   if (signal_pending_state(state, current))
>   break;
>  
> -- 
> 2.11.0
>
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[Intel-gfx] [PATCH] drm/i915: Break i915_spin_request() if we see an interrupt

[Chris Wilson]

If an interrupt has been posted, and we were spinning on the active
seqno waiting for it to advance but it did not, then we can expect that
it will not see its advance in the immediate future and should call into
the irq-seqno barrier. We can stop spinning at this point, and leave the
difficulty of handling the coherency to the caller.

Signed-off-by: Chris Wilson 
Cc: Tvrtko Ursulin 
---
 drivers/gpu/drm/i915/i915_gem_request.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gem_request.c 
b/drivers/gpu/drm/i915/i915_gem_request.c
index 7760d7481f85..9e42b2687cae 100644
--- a/drivers/gpu/drm/i915/i915_gem_request.c
+++ b/drivers/gpu/drm/i915/i915_gem_request.c
@@ -993,6 +993,9 @@ bool __i915_spin_request(const struct drm_i915_gem_request 
*req,
  seqno))
return true;
 
+   if (test_bit(ENGINE_IRQ_BREADCRUMB, >engine->irq_posted))
+   break;
+
if (signal_pending_state(state, current))
break;
 
-- 
2.11.0

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