[Intel-gfx] [PATCH 03/18] drm/i915: "Race-to-idle" after switching to the kernel context

[Mika Kuoppala]

Chris Wilson <chris at chris-wilson.co.uk> writes:

> During suspend we want to flush out all active contexts and their
> rendering. To do so we queue a request from the kernel's context, once
> we know that request is done, we know the GPU is completely idle. To
> speed up that switch bump the GPU clocks.
>
> Switching to the kernel context prior to idling is also used to enforce
> a barrier before changing OA properties, and when evicting active
> rendering from the global GTT. All cases where we do want to
> race-to-idle.
>
> v2: Limit the boosting to only the switch before suspend.
> v3: Limit it to the wait-for-idle on suspend.
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: David Weinehall <david.weinehall at linux.intel.com>
> Cc: Mika Kuoppala <mika.kuoppala at intel.com>
> Reviewed-by: Mika Kuoppala <mika.kuoppala at intel.com> #v1
> Tested-by: David Weinehall <david.weinehall at linux.intel.com> #v1
> ---
>  drivers/gpu/drm/i915/i915_gem.c     | 27 +++++++++++++++++++++++++--
>  drivers/gpu/drm/i915/i915_request.h |  1 +
>  2 files changed, 26 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index c93f5dcb1d82..7b5544efa0ba 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -3704,7 +3704,29 @@ i915_gem_wait_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
>  
>  static int wait_for_timeline(struct i915_timeline *tl, unsigned int flags)
>  {
> -	return i915_gem_active_wait(&tl->last_request, flags);
> +	struct i915_request *rq;
> +	long ret;
> +
> +	rq = i915_gem_active_get_unlocked(&tl->last_request);
> +	if (!rq)
> +		return 0;
> +
> +	/*
> +	 * "Race-to-idle".
> +	 *
> +	 * Switching to the kernel context is often used a synchronous
> +	 * step prior to idling, e.g. in suspend for flushing all
> +	 * current operations to memory before sleeping. These we
> +	 * want to complete as quickly as possible to avoid prolonged
> +	 * stalls, so allow the gpu to boost to maximum clocks.
> +	 */
> +	if (flags & I915_WAIT_FOR_IDLE_BOOST)
> +		gen6_rps_boost(rq, NULL);
> +
> +	ret = i915_request_wait(rq, flags, MAX_SCHEDULE_TIMEOUT);

I pondered about the boost flag falling through into wait.
But they are flags on wait domain so no reason to split/limit.

Reviewed-by: Mika Kuoppala <mika.kuoppala at linux.intel.com>

> +	i915_request_put(rq);
> +
> +	return ret < 0 ? ret : 0;
>  }
>  
>  static int wait_for_engines(struct drm_i915_private *i915)
> @@ -4979,7 +5001,8 @@ int i915_gem_suspend(struct drm_i915_private *dev_priv)
>  
>  		ret = i915_gem_wait_for_idle(dev_priv,
>  					     I915_WAIT_INTERRUPTIBLE |
> -					     I915_WAIT_LOCKED);
> +					     I915_WAIT_LOCKED |
> +					     I915_WAIT_FOR_IDLE_BOOST);
>  		if (ret && ret != -EIO)
>  			goto err_unlock;
>  
> diff --git a/drivers/gpu/drm/i915/i915_request.h b/drivers/gpu/drm/i915/i915_request.h
> index 1bbbb7a9fa03..491ff81d0fea 100644
> --- a/drivers/gpu/drm/i915/i915_request.h
> +++ b/drivers/gpu/drm/i915/i915_request.h
> @@ -267,6 +267,7 @@ long i915_request_wait(struct i915_request *rq,
>  #define I915_WAIT_INTERRUPTIBLE	BIT(0)
>  #define I915_WAIT_LOCKED	BIT(1) /* struct_mutex held, handle GPU reset */
>  #define I915_WAIT_ALL		BIT(2) /* used by i915_gem_object_wait() */
> +#define I915_WAIT_FOR_IDLE_BOOST BIT(3)
>  
>  static inline u32 intel_engine_get_seqno(struct intel_engine_cs *engine);
>  
> -- 
> 2.17.0