On ti, 2016-04-26 at 13:57 +0100, Chris Wilson wrote: > On Tue, Apr 26, 2016 at 03:44:22PM +0300, Imre Deak wrote: > > Setting a write-back cache policy in the MOCS entry definition also > > implies snooping, which has a considerable overhead. This is > > unexpected for a few reasons: > > If it is snooping, then I don't see why it is undesirable to have it > available in a mocs setting. If it is bogus and the bit is undefined, > then by all means remove it. None of these entries are used alone for coherent surfaces. For that the application would have to use entry index#1 or #2 _and_ call the set caching IOCTL to set the corresponding buffer to be cached. The problem is that without setting the buffer to be cacheable the expectation is that we won't be snooping and incur the corresponding overhead. This is what this patch addresses. The bit is also bogus, if we wanted snooping via MOCS we'd use the dedicated HW flag for that. If we wanted to have a snooping MOCS entry we should add that separately (as a forth entry), but we'd need this change as a fix for current users. --Imre _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
