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

[Tvrtko Ursulin]

On 27/09/2023 20:34, Belgaumkar, Vinay wrote:
> 
> On 9/21/2023 3:41 AM, Tvrtko Ursulin wrote:
>>
>> 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?
> We have asked Carl (cc'd) to post a patch for the same.

Ack.

>>> Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
>>> Signed-off-by: Vinay Belgaumkar <vinay.belgaumkar at 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?
> sure.
>>
>> 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.
> 
> Makes sense. We could add a SET_DEADLINE flag or something similar and 
> pass in the deadline when appropriate.

Rob - do you have time and motivation to think about this angle at all 
currently? If not I guess we just proceed with the new flag for our 
GEM_WAIT.

Regards,

Tvrtko

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