Re: [PATCH 00/13] Gen7 batch buffer command parser

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Jan 29, 2014 at 02:22:49PM -0800, Volkin, Bradley D wrote:
> On Wed, Jan 29, 2014 at 02:11:17PM -0800, Daniel Vetter wrote:
> > On Wed, Jan 29, 2014 at 01:55:01PM -0800, bradley.d.volkin@intel.com wrote:
> > > From: Brad Volkin <bradley.d.volkin@intel.com>
> > > 3) Coherency. I've found a coherency issue on VLV when reading the batch buffer
> > >    from the CPU during execbuffer2. Userspace writes the batch via pwrite fast
> > >    path before calling execbuffer2. The parser reads stale data. This works fine
> > >    on IVB and HSW, so I believe it's an LLC vs. non-LLC issue. I'm just unclear
> > >    on what the correct flushing or synchronization is for this scenario. This
> > >    only matters if we get PPGTT working on VLV and enable the parser there.
> > 
> > Hm, adopting the shmem_read clflushing didn't help for this? That would be
> > fairly shocking, since it means our shmem read paths are broken. Which are
> > used e.g. by the libva readback code for the encoded bitstream.
> 
> Sorry, not clear enough. I actually haven't retested that part with the clflushing
> added since the opinion seemed to be that leaving the parser disabled for VLV was ok.
> Just left the note for now so it doesn't get lost.

Would be nice to give it spin though, since afaik this issue might persist
on vlv+1. And I guess we can't keep on sticking our heads into sand about
ppgtt not really working on soc platforms ;-)
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch