On Friday, September 26, 2014 04:41:14 PM Chris Wilson wrote: > On Fri, Sep 26, 2014 at 08:36:39AM -0700, Kristian Høgsberg wrote: > > On Fri, Aug 29, 2014 at 11:10:49PM -0700, Kenneth Graunke wrote: > > > We don't really want extra buffer copying or stalls when mapping, > > > so it'd be nice to know when it's happening. > > > > > > Signed-off-by: Kenneth Graunke <kenn...@whitecape.org> > > > > Reviewed-by: Kristian Høgsberg <k...@bitplanet.net> > > This warns if the the program cache is currently being read by the GPU > (expected) but a read-read (as used here) does not incur a stall. > -Chris
Good catch! Since we're doing a read-only mapping, and all of our relocations to this buffer have 0 for the write domains, GEM knows that nobody is altering it, so there shouldn't be a stall. Even though i915_gem_set_domain_ioctl calls i915_gem_object_wait_rendering__nonblocking, it shouldn't actually wait. Thanks for spotting this. I'll drop this hunk. I suppose this is a problem with my stall-warning code in general... drm_intel_bo_busy() == true does not necessarily imply that there will be a stall when mapping it. I hadn't considered that. It sounds like patch 4 (using unsynchronized mappings) is still useful though, as drm_intel_bo_subdata/pwrite doesn't know that it's safe to let the CPU write the buffer even while the GPU is reading it. --Ken
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