Re: [Intel-gfx] [PATCH] drm/i915/gem: Allow users to disable waitboost

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

On 20/09/2023 22:56, Vinay Belgaumkar wrote:
> Provide a bit to disable waitboost while waiting on a gem object.
> Waitboost results in increased power consumption by requesting RP0
> while waiting for the request to complete. Add a bit in the gem_wait()
> IOCTL where this can be disabled.
> 
> This is related to the libva API change here -
> Link: https://github.com/XinfengZhang/libva/commit/3d90d18c67609a73121bb71b20ee4776b54b61a7

This link does not appear to lead to userspace code using this uapi?

> 
> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> Signed-off-by: Vinay Belgaumkar <vinay.belgaumkar@intel.com>
> ---
>   drivers/gpu/drm/i915/gem/i915_gem_wait.c | 9 ++++++---
>   drivers/gpu/drm/i915/i915_request.c      | 3 ++-
>   drivers/gpu/drm/i915/i915_request.h      | 1 +
>   include/uapi/drm/i915_drm.h              | 1 +
>   4 files changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_wait.c b/drivers/gpu/drm/i915/gem/i915_gem_wait.c
> index d4b918fb11ce..955885ec859d 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_wait.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_wait.c
> @@ -72,7 +72,8 @@ i915_gem_object_wait_reservation(struct dma_resv *resv,
>   	struct dma_fence *fence;
>   	long ret = timeout ?: 1;
>   
> -	i915_gem_object_boost(resv, flags);
> +	if (!(flags & I915_WAITBOOST_DISABLE))
> +		i915_gem_object_boost(resv, flags);
>   
>   	dma_resv_iter_begin(&cursor, resv,
>   			    dma_resv_usage_rw(flags & I915_WAIT_ALL));
> @@ -236,7 +237,7 @@ i915_gem_wait_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
>   	ktime_t start;
>   	long ret;
>   
> -	if (args->flags != 0)
> +	if (args->flags != 0 || args->flags != I915_GEM_WAITBOOST_DISABLE)
>   		return -EINVAL;
>   
>   	obj = i915_gem_object_lookup(file, args->bo_handle);
> @@ -248,7 +249,9 @@ i915_gem_wait_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
>   	ret = i915_gem_object_wait(obj,
>   				   I915_WAIT_INTERRUPTIBLE |
>   				   I915_WAIT_PRIORITY |
> -				   I915_WAIT_ALL,
> +				   I915_WAIT_ALL |
> +				   (args->flags & I915_GEM_WAITBOOST_DISABLE ?
> +				    I915_WAITBOOST_DISABLE : 0),
>   				   to_wait_timeout(args->timeout_ns));
>   
>   	if (args->timeout_ns > 0) {
> diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
> index f59081066a19..2957409b4b2a 100644
> --- a/drivers/gpu/drm/i915/i915_request.c
> +++ b/drivers/gpu/drm/i915/i915_request.c
> @@ -2044,7 +2044,8 @@ long i915_request_wait_timeout(struct i915_request *rq,
>   	 * but at a cost of spending more power processing the workload
>   	 * (bad for battery).
>   	 */
> -	if (flags & I915_WAIT_PRIORITY && !i915_request_started(rq))
> +	if (!(flags & I915_WAITBOOST_DISABLE) && (flags & I915_WAIT_PRIORITY) &&
> +	    !i915_request_started(rq))
>   		intel_rps_boost(rq);
>   
>   	wait.tsk = current;
> diff --git a/drivers/gpu/drm/i915/i915_request.h b/drivers/gpu/drm/i915/i915_request.h
> index 0ac55b2e4223..3cc00e8254dc 100644
> --- a/drivers/gpu/drm/i915/i915_request.h
> +++ b/drivers/gpu/drm/i915/i915_request.h
> @@ -445,6 +445,7 @@ long i915_request_wait(struct i915_request *rq,
>   #define I915_WAIT_INTERRUPTIBLE	BIT(0)
>   #define I915_WAIT_PRIORITY	BIT(1) /* small priority bump for the request */
>   #define I915_WAIT_ALL		BIT(2) /* used by i915_gem_object_wait() */
> +#define I915_WAITBOOST_DISABLE	BIT(3) /* used by i915_gem_object_wait() */
>   
>   void i915_request_show(struct drm_printer *m,
>   		       const struct i915_request *rq,
> diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
> index 7000e5910a1d..4adee70e39cf 100644
> --- a/include/uapi/drm/i915_drm.h
> +++ b/include/uapi/drm/i915_drm.h
> @@ -1928,6 +1928,7 @@ struct drm_i915_gem_wait {
>   	/** Handle of BO we shall wait on */
>   	__u32 bo_handle;
>   	__u32 flags;
> +#define I915_GEM_WAITBOOST_DISABLE      (1u<<0)

Probably would be good to avoid mentioning waitboost in the uapi since 
so far it wasn't an explicit feature/contract. Something like 
I915_GEM_WAIT_BACKGROUND_PRIORITY? Low priority?

I also wonder if there could be a possible angle to help Rob (+cc) 
upstream the syncobj/fence deadline code if our media driver might make 
use of that somehow.

Like if either we could wire up the deadline into GEM_WAIT (in a 
backward compatible manner), or if media could use sync fd wait instead. 
Assuming they have an out fence already, which may not be true.

Regards,

Tvrtko

>   	/** Number of nanoseconds to wait, Returns time remaining. */
>   	__s64 timeout_ns;
>   };