Re: [PATCH 09/10] drm/i915/execlist: Trim immediate timeslice expiry

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

On 14/10/2019 23:05, Chris Wilson wrote:
> We perform timeslicing immediately upon receipt of a request that may be
> put into the second ELSP slot. The idea behind this was that since we
> didn't install the timer if the second ELSP slot was empty, we would not
> have any idea of how long ELSP[0] had been running and so giving the
> newcomer a chance on the GPU was fair. However, this causes us extra
> busy work that we may be able to avoid if we wait a jiffie for the first
> timeslice as normal.
 >
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>   drivers/gpu/drm/i915/gt/intel_lrc.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
> index 60e897c000b2..f9bf78032ad7 100644
> --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> @@ -1613,7 +1613,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>   			last->hw_context->lrc_desc |= CTX_DESC_FORCE_RESTORE;
>   			last = NULL;
>   		} else if (need_timeslice(engine, last) &&
> -			   !timer_pending(&engine->execlists.timer)) {
> +			   timer_expired(&engine->execlists.timer)) {

timer_expired is !timer_pending(..) && t->expires. Presumably that means 
it was scheduled at least once in the past but currently isn't. Then 
immediately after the first timer the t->expires check becomes useless? 
I must be missing something.. Oh, you have piggy-backed some custom code 
to timers.. hm.. Looks like it would work.

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko

>   			GEM_TRACE("%s: expired last=%llx:%lld, prio=%d, hint=%d\n",
>   				  engine->name,
>   				  last->fence.context,
> @@ -2074,6 +2074,8 @@ static void process_csb(struct intel_engine_cs *engine)
>   
>   			if (enable_timeslice(execlists))
>   				mod_timer(&execlists->timer, jiffies + 1);
> +			else
> +				cancel_timer(&execlists->timer);
>   
>   			WRITE_ONCE(execlists->pending[0], NULL);
>   		} else {
> @@ -3591,7 +3593,7 @@ gen12_emit_fini_breadcrumb_rcs(struct i915_request *request, u32 *cs)
>   
>   static void execlists_park(struct intel_engine_cs *engine)
>   {
> -	del_timer(&engine->execlists.timer);
> +	cancel_timer(&engine->execlists.timer);
>   	cancel_timer(&engine->execlists.preempt);
>   }
>   
> 
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