Re: [PATCH 13/19] drm/i915/gt: Move new timelines to the end of active_list

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

On 18/11/2019 23:02, Chris Wilson wrote:
> When adding a new active timeline, place it at the end of the list. This
> allows for intel_gt_retire_requests() to pick up the newcomer more
> quickly and hopefully complete the retirement sooner.
> 
> References: 7936a22dd466 ("drm/i915/gt: Wait for new requests in intel_gt_retire_requests()")
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> ---
>   drivers/gpu/drm/i915/gt/intel_timeline.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_timeline.c b/drivers/gpu/drm/i915/gt/intel_timeline.c
> index bd973d950064..b190a5d9ab02 100644
> --- a/drivers/gpu/drm/i915/gt/intel_timeline.c
> +++ b/drivers/gpu/drm/i915/gt/intel_timeline.c
> @@ -359,7 +359,7 @@ void intel_timeline_enter(struct intel_timeline *tl)
>   
>   	spin_lock(&timelines->lock);
>   	if (!atomic_fetch_inc(&tl->active_count))
> -		list_add(&tl->link, &timelines->active_list);
> +		list_add_tail(&tl->link, &timelines->active_list);
>   	spin_unlock(&timelines->lock);
>   }
>   
> 

If I am not missing something this should be on the micro-optimisation 
level, well, mini-optimisation. Since for instance now it could wait on 
the most recent request and when that finishes do mostly signalled 
checks, or even less. With the change it would first sweep the already 
completed ones and then wait for the most recent one. Nevertheless, I 
don't see a problem with it so:

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

Regards,

Tvrtko
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