[Intel-gfx] [PATCH v2 3/6] drm/i915/guc: use a separate GuC client for each engine

[Dave Gordon]

On 21/07/16 19:30, Chris Wilson wrote:
> On Thu, Jul 21, 2016 at 07:15:39PM +0100, Dave Gordon wrote:
>> When using a single GuC client for multiple engines, the i915 driver has
>> to merge all work items into a single work queue, which the GuC firmware
>> then demultiplexes into separate submission queues per engine. In
>> theory, this could lead to the single queue becoming a bottleneck in
>> which an excess of outstanding work for one or more engines might
>> prevent work for an idle engine reaching the hardware.
>>
>> To reduce this risk, we can create one GuC client per engine. Each will
>> have its own workqueue, to be used only for work targeting a single
>> engine, so there will be no cross-engine contention for workqueue slots.
>>
>> Signed-off-by: Dave Gordon <david.s.gordon at intel.com>
>> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
>
> Does guc_context_desc.engines_used have any effect?
> -Chris

Yes, some of the firmware code uses it to optimise which queues it scans 
at certain times. If it knows that a certain queue *doesn't* contain 
work for a given engine, it can skip scanning that queue entirely.

Does this patchset change the results in the parallel-submission nop test?

.Dave.