[Intel-gfx] [PATCH 08/64] drm/i915: Retire oldest completed request before allocating next

[Chris Wilson]

On Thu, Jul 07, 2016 at 10:41:03AM +0100, Tvrtko Ursulin wrote:
> 
> On 07/07/16 09:41, Chris Wilson wrote:
> >In order to keep the memory allocated for requests reasonably tight, try
> >to reuse the oldest request (so long as it is completed and has no
> >external references) for the next allocation.
> >
> >Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> >---
> >  drivers/gpu/drm/i915/i915_gem_request.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> >diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
> >index 9e9aa6b725f7..ee1189c35509 100644
> >--- a/drivers/gpu/drm/i915/i915_gem_request.c
> >+++ b/drivers/gpu/drm/i915/i915_gem_request.c
> >@@ -226,6 +226,13 @@ __i915_gem_request_alloc(struct intel_engine_cs *engine,
> >  	if (ret)
> >  		return ret;
> >
> >+	if (!list_empty(&engine->request_list)) {
> >+		req = list_first_entry(&engine->request_list,
> >+				       typeof(*req), list);
> >+		if (i915_gem_request_completed(req))
> >+			i915_gem_request_retire(req);
> >+	}
> >+
> >  	req = kmem_cache_zalloc(dev_priv->requests, GFP_KERNEL);
> >  	if (!req)
> >  		return -ENOMEM;
> >
> 
> I am thinking that this does not play well with the execlists which
> is holding references to requests for a little bit longer than they
> are on the engine->request_list.
> 
> In fact I don't see how you can just steal it without looking at the
> reference count.

?

There is no stealing, the request list and execlist are independently
referenced.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre