On Sun, Dec 29, 2013 at 09:59:26AM +0000, Chris Wilson wrote: > On Sat, Dec 28, 2013 at 01:31:49PM -0800, Ben Widawsky wrote: > > The initialized flag is used to specify a context has been initialized > > and it's context is safe to load, ie. the 3d state is setup properly. > > With full PPGTT, we emit the address space loads during context switch > > and this currently marks a context as initialized. With full PPGTT > > patches, if a client first emits a batch to !RCS, then later, RCS, the > > code will mistake the context as initialized and try to reload an > > uninitialized context. > > > > 1. context 1 blit // context initialized > +context marked as initialised > > > 2. context 2 <X operation> // saves context 1 random state > > 3. context 1 render // loads random state from step 2 > > Note that step 2 is not required since the tracking is per-ring. > This is missing an extremely important caveat which I was incorrectly correlating earlier in our discussion. Yes, step 2 is not required. The step which is required is the page allocated must be non-zero when allocated, and the contents of the page must be capable of hanging the GPU when used as a context object. Otherwise, the uninitialized context would always be all 0, which if I understand the HW correctly, is "safe" As long as you don't disagree, I'll fix the commit message with that info. > > It is really easy to hit this with a planned upcoming patch which makes > > default context reuse possible. > > > > NOTE: This should only effect full PPGTT branches, ie. current > > drm-intel-nightly. > > Though we did postulate that mesa could hit this in a pathological > scenario with a freshly created context. > > > Thanks to Chris for helping me track this down. > > > > Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > > Signed-off-by: Ben Widawsky <ben@xxxxxxxxxxxx> > Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > -Chris > > -- > Chris Wilson, Intel Open Source Technology Centre -- Ben Widawsky, Intel Open Source Technology Center _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
