Re: [igt-dev] [PATCH i-g-t v2 08/10] tests/i915/exec_fence: add timeline fence tests

Lionel Landwerlin
2019-11-22T16:03:19Z

On 22/11/2019 17:51, Chris Wilson wrote:
> Quoting Lionel Landwerlin (2019-11-22 15:43:11)
>> On 22/11/2019 17:26, Chris Wilson wrote:
>>> Quoting Lionel Landwerlin (2019-11-22 13:02:58)
>>>> We can now give a tuple (handle, point_value) for timeline semaphores.
>>>>
>>>> v2: Fix up syncobj-timeline-repeat test (Lionel)
>>>> Update following kernel rename
>>>>
>>>> v3: Add more ordering tests for syncobj/buffer handle state (Chris)
>>> Another question, do we worry about sw_sync imported fences being
>>> handles differently to native?
>>> -Chris
>> What do you mean by differently?
> We have is_i915_fence() with branching paths for internal/external, and
> within the syncobj timeline mixed fence contexts cause a hard barrier,
> so may present interesting effects at the uAPI layer?

Well... same issues with an array of i915 fences right?

I guess fence_set_priority() could be adjusted to deal with
dma-fence-chain like it does with dma-fence-array.

-Lionel

>
>> Thing is sw_sync can delay the signaling forever so you could build a
>> case exhausting memory if you really wanted.
> Except we don't allow indefinite waits for external fences such as
> sw_sync and wrap them in auto-expiring fences.
>
>> Whereas my understand of other dma-fences is that they should be short
>> lived.
> Endless. How's that going to end? Badly.
> -Chris