From mboxrd@z Thu Jan  1 00:00:00 1970
From: Daniel Vetter <daniel@ffwll.ch>
Subject: Re: [PATCH 37/48] drm/i915: Defer request freeing
Date: Wed, 18 Dec 2013 15:39:33 +0100
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To: Chris Wilson <chris@chris-wilson.co.uk>, Ben Widawsky <benjamin.widawsky@intel.com>, Intel GFX <intel-gfx@lists.freedesktop.org>, Ben Widawsky <ben@bwidawsk.net>
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On Thu, Dec 12, 2013 at 11:08:47AM +0000, Chris Wilson wrote:
> On Fri, Dec 06, 2013 at 02:11:22PM -0800, Ben Widawsky wrote:
> > From: Ben Widawsky <ben@bwidawsk.net>
> > 
> > With context destruction, we always want to be able to tear down the
> > underlying address space. This is invoked on the last unreference to the
> > context which could happen before we've moved all objects to the
> > inactive list. To enable a clean tear down the address space, make sure
> > to process the request free lastly.
> > 
> > Without this change, we cannot guarantee to we don't still have active
> > objects in the VM.
> > 
> > As an example of a failing case:
> > CTX-A is created, count=1
> > CTX-A is used during execbuf
> > 	does a context switch count = 2
> > 	and add_request count = 3
> > CTX B runs, switches, CTX-A count = 2
> > CTX-A is destroyed, count = 1
> > retire requests is called
> > 	free_request from CTX-A, count = 0 <--- free context with active object
> > 
> > As mentioned above, by doing the free request after processing the
> > active list, we can avoid this case.
> 
> So just process the active_list first, the requests and objects
> associated with the ring should be fairly independent.

Also, stuff like this needs a testcase, and I didn't spot such a thing in
the patches posted thus far.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch