[Intel-gfx] [PATCH] drm/i915/gt: Ratelimit display power w/a

[Tvrtko Ursulin]

On 18/12/2019 09:35, Chris Wilson wrote:
> For very light workloads that frequently park, acquiring the display
> power well (required to prevent the dmc from trashing the system) takes
> longer than the execution. A good example is the igt_coherency selftest,
> which is slowed down by an order of magnitude in the worst case with
> powerwell cycling. To prevent frequent cycling, while keeping our fast
> soft-rc6, use a timer to delay release of the display powerwell.
> 
> Fixes: 311770173fac ("drm/i915/gt: Schedule request retirement when timeline idles")
> References: https://gitlab.freedesktop.org/drm/intel/issues/848
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> ---
>   drivers/gpu/drm/i915/gt/intel_gt_pm.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_gt_pm.c b/drivers/gpu/drm/i915/gt/intel_gt_pm.c
> index bb57e3443a50..f36ce36dabeb 100644
> --- a/drivers/gpu/drm/i915/gt/intel_gt_pm.c
> +++ b/drivers/gpu/drm/i915/gt/intel_gt_pm.c
> @@ -88,8 +88,9 @@ static int __gt_park(struct intel_wakeref *wf)
>   	/* Everything switched off, flush any residual interrupt just in case */
>   	intel_synchronize_irq(i915);
>   
> +	/* Defer dropping the display power well for 100ms, it's slow! */
>   	GEM_BUG_ON(!wakeref);
> -	intel_display_power_put(i915, POWER_DOMAIN_GT_IRQ, wakeref);
> +	intel_display_power_put_async(i915, POWER_DOMAIN_GT_IRQ, wakeref);
>   
>   	i915_globals_park();
>   
> 

Checked that intel_display_power_get cancels the delayed put since I 
wasn't familiar with the API and it looks good.

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

Regards,

Tvrtko