[Intel-gfx] [PATCH 3/3] drm/ttm: remove ttm_bo_wait_unreserved

[Koenig, Christian]

Am 21.08.19 um 16:47 schrieb Daniel Vetter:
> On Wed, Aug 21, 2019 at 4:27 PM Thomas Hellström (VMware)
> <thomas_os at shipmail.org> wrote:
>> On 8/21/19 4:09 PM, Daniel Vetter wrote:
>>> On Wed, Aug 21, 2019 at 2:47 PM Thomas Hellström (VMware)
>>> <thomas_os at shipmail.org> wrote:
>>>> On 8/21/19 2:40 PM, Thomas Hellström (VMware) wrote:
>>>>> On 8/20/19 4:53 PM, Daniel Vetter wrote:
>>>>> [SNIP]
>> but to keep the mm latency optimization using the RETRY functionality:
> Still no idea why this is needed? All the comments here and the code
> and history seem like they've been about the mmap_sem vs dma_resv
> inversion between driver ioctls and fault handling here. Once that's
> officially fixed there's no reason to play games here and retry loops
> - previously that was necessary because the old ttm_bo_vm_fault had a
> busy spin and that's definitely not nice. If it's needed I think it
> should be a second patch on top, to keep this all clear. I had to
> audit an enormous amount of code, I'd like to make sure I didn't miss
> anything before we start to make this super fancy again. Further
> patches on top is obviously all fine with me.

I think this is just an optimization to not hold the mmap_sem while 
waiting for the dma_resv lock.

I agree that it shouldn't be necessary, but maybe it's a good idea for 
performance. I'm also OK with removing it, cause I'm not sure if it's 
worth it.

But Thomas noted correctly that we should probably do it in a separate 
patch so that when somebody points out "Hey my system is slower now!" 
he's able to bisect to the change.

Christian.

> -Daniel
>
>> Thanks,
>> Thomas
>>