[PATCH 17/19] drm/radeon: use rcu waits in some ioctls

[Michel Dänzer]

On 04.08.2014 17:56, Maarten Lankhorst wrote:
> op 04-08-14 10:42, Michel Dänzer schreef:
>> On 02.08.2014 02:07, Maarten Lankhorst wrote:
>>> On 01-08-14 16:13, Michel Dänzer wrote:
>>>> On 01.08.2014 19:12, Maarten Lankhorst wrote:
>>>>> On 01-08-14 10:27, Michel Dänzer wrote:
>>>>>> On 01.08.2014 00:34, Maarten Lankhorst wrote:
>>>>>>> @@ -357,14 +360,20 @@ int radeon_gem_wait_idle_ioctl(struct drm_device *dev, void *data,
>>>>>>>  	struct drm_radeon_gem_wait_idle *args = data;
>>>>>>>  	struct drm_gem_object *gobj;
>>>>>>>  	struct radeon_bo *robj;
>>>>>>> -	int r;
>>>>>>> +	int r = 0;
>>>>>>> +	long ret;
>>>>>>>  
>>>>>>>  	gobj = drm_gem_object_lookup(dev, filp, args->handle);
>>>>>>>  	if (gobj == NULL) {
>>>>>>>  		return -ENOENT;
>>>>>>>  	}
>>>>>>>  	robj = gem_to_radeon_bo(gobj);
>>>>>>> -	r = radeon_bo_wait(robj, NULL, false);
>>>>>>> +	ret = reservation_object_wait_timeout_rcu(robj->tbo.resv, true, true, 30 * HZ);
>>>>>>> +	if (ret == 0)
>>>>>>> +		r = -EBUSY;
>>>>>>> +	else if (ret < 0)
>>>>>>> +		r = ret;
>>>>>>> +
>>>>>>>  	/* callback hw specific functions if any */
>>>>>>>  	if (rdev->asic->ioctl_wait_idle)
>>>>>>>  		robj->rdev->asic->ioctl_wait_idle(rdev, robj);
>>>>>> Heads up, this conflicts with
>>>>>> http://lists.freedesktop.org/archives/dri-devel/2014-August/065255.html
>>>>>> which passes a non-NULL second argument to radeon_bo_wait() to get the
>>>>>> BO's current domain.
>>>>> Ok, I will fix it up and resend it later.
>>>>>
>>>>> Does it matter if I grab the current domain without grabbing the lock
>>>>> here? Because it doesn't matter if it sees the old or new domain, it
>>>>> could have been changed after returning too.
>>>> It should be the domain where the BO is located when the fence we are
>>>> waiting for here signals.
>>> Could we compare domain before and after the rcu wait, and retry
>>> waiting if they're different, and the new one is VRAM? (eg eviction
>>> happened) That should prevent needing to lock the bo.
>> Eviction normally only happens from VRAM, not to VRAM. :) So if you know
>> whether the domain is VRAM or not after the wait, you can just proceed
>> accordingly, I don't see why you'd need to wait again.
> Because in the worst case you didn't wait on the fence that started
> the eviction, but one before it. ;-)

I'm afraid you've lost me. Can you determine the domain that
radeon_bo_wait() would have returned?


-- 
Earthling Michel Dänzer            |                  http://www.amd.com
Libre software enthusiast          |                Mesa and X developer