[Intel-gfx] [PATCH] drm/i915: Keep ring->active_list and ring->requests_list consistent

[Chris Wilson]

On Fri, Mar 20, 2015 at 04:00:50PM +0100, Daniel Vetter wrote:
> On Fri, Mar 20, 2015 at 02:45:04PM +0000, Chris Wilson wrote:
> > On Fri, Mar 20, 2015 at 03:32:52PM +0100, Daniel Vetter wrote:
> > > But if we do that short-circuiting in ring_idle the all the requests
> > > _should_ be completed. Which meanse retire_request_ring should move all
> > > buffers to the inactive list, even when we do that before retiring
> > > requests.
> > 
> > We test for the requests to be retired after we test for the buffers to
> > be retired. It is very easy then for us to have active buffers as the
> > seqno advanced after the buffer retirement and before the requests. That
> > is (one of) the reasons why we previously sampled seqno only once when
> > retiring buffers + requests.
> 
> Yeah I get that part of the race. But before we retire anything in these
> callsites we call gpu_idle. And that waits for everything to complete,
> except whent there are not outstanding requests (i.e. ->request_list is
> empyt). So either
> - ->request_list is empty in ring_idle, which means all requests should
>   have completed.  Even if there are some lingering active buffers still
>   around we should clean them up.
> - ->request_list is not empty, in which case we do a full wait for the
>   most recent request. Again all requests should have completed and we
>   should be able to clean out both request and active lists.
> 
> I do see how we can get out of the retire_request functions with requests
> empty but still active buffers around. But I don't understand how that's
> possible with a gpu_idle in front. And thus far all traces are from places
> where we do call gpu_idle first.
> 
> Or am I missing something?

The retire comes before the before the gpu_idle (we retire often as a
part of busy, execbuffer, timers etc). The traces show exactly that.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre