Re: [PATCH 4/4] drm/i915: Remove the spin-request during execbuf await_request

[Joonas Lahtinen <joonas.lahtinen@linux.intel.com>]

On ma, 2017-06-05 at 11:26 +0100, Chris Wilson wrote:
> Originally we would enable and disable the breadcrumb interrupt
> immediately on demand. This was slow enough to have a large impact
> (>30%) on tasks that hopped between engines. However, by using a shadow
> to keep the irq alive for an extra interrupt (see commit 67b807a89230
> ("drm/i915: Delay disabling the user interrupt for breadcrumbs")) and
> by recently reducing the cost in adding ourselves to the signal tree, we
> no longer need to spin-request during await_request to avoid delays in
> throughput tests. Without the earlier patches to stop the wakeup when
> signaling if the irq was already active, we saw no improvement in
> execbuf overhead (and corresponding contention in other clients) despite
> the removal of the spinner in a simple test like glxgears. This means
> that will be scenarios where now we spend longer enabling the interrupt

      ^ there ?          "now where we" ? 

> than we would have spent spinning, but these are not likely to have as
> noticeable an impact as the high frequency test cases (where there
> should not be any regression).
> 
> Ulterior motive: generalising the engine->sync_to to handle different
> types of semaphores and non-semaphores.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Oscar Mateo <oscar.mateo@intel.com>

Does what is described, so code itself is:

Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

Some Testcase:'s would be cool, without those it's bit handwavy. Maybe
an Ack from Tvrtko.

Regards, Joonas
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation
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