Re: [PATCH 2/2] drm/i915: Postpone fake breadcrumb interrupt if a real interrupt is pending

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 16/02/2017 09:29, Chris Wilson wrote:
> If the timer expires for enabling the fake interrupt, check to see
> if there is a real interrupt queued before making the decision to start
> polling. This helps in situations where we have a very slow irq-seqno
> barrier that may accrue more breadcrumb interrupts before it is able to
> catch up. It still leaves a hole for the timer to expire as we are
> processing the last irq-seqno barrier, but it appears to help reduce the
> frequency of "missed-interrupts" on Ironlake, at least.
>
> References: https://bugs.freedesktop.org/show_bug.cgi?id=99816
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_breadcrumbs.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
> index ef3adfd37d7d..21269421bd2a 100644
> --- a/drivers/gpu/drm/i915/intel_breadcrumbs.c
> +++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
> @@ -41,6 +41,11 @@ static void intel_breadcrumbs_hangcheck(unsigned long data)
>  		return;
>  	}
>
> +	if (test_bit(ENGINE_IRQ_BREADCRUMB, &engine->irq_posted)) {
> +		mod_timer(&b->hangcheck, jiffies + 1);
> +		return;
> +	}
> +
>  	DRM_DEBUG("Hangcheck timer elapsed... %s idle\n", engine->name);
>  	set_bit(engine->id, &engine->i915->gpu_error.missed_irq_rings);
>  	mod_timer(&engine->breadcrumbs.fake_irq, jiffies + 1);
>

Another hmm :), barriers are so much shorter than the hangcheck interval 
(1500ms) so I don't quite understand what is the problem.

Should we instead put a mod_timer when raising the user irq?

Regards,

Tvrtko
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