Quoting Chris Wilson (2018-06-10 22:43:11) > The discovery with trying to enable full-ppgtt was that we were > completely failing to the load both the mm and context following the > reset. Although we were performing mmio to set the PP_DIR (per-process > GTT) and CCID (context), these were taking no effect (the assumption was > that this would trigger reload of the context and restore the page > tables). It was not until we performed the LRI + MI_SET_CONTEXT in a > following context switch would anything occur. > > Since we are then required to reset the context image and PP_DIR using > CS commands, we place those commands into every batch. The hardware > should recognise the no-ops and eliminate the expensive context loads, > but we still have to pay the cost of using cross-powerwell register > writes. In practice, this has no effect on actual context switch times, > and only adds a few hundred nanoseconds to no-op switches. We can improve > the latter by eliminating the w/a around known no-op switches, but there > is an ulterior motive to keeping them. > > Always emitting the context switch at the beginning of the request (and > relying on HW to skip unneeded switches) does have one key advantage. > Should we implement request reordering on Haswell, we will not know in > advance what the previous executing context was on the GPU and so we > would not be able to elide the MI_SET_CONTEXT commands ourselves and > always have to emit them. Having our hand forced now actually prepares > us for later. Please comment about the destiny of the tracepoint for the sake of the bisecter that will end up here to look for a lost tracepoint :) Also, you could throw a Testcase: this affects. > > v2: Sandybridge has to agree to use LRI as well. > > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx> > Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx> > Cc: Matthew Auld <matthew.william.auld@xxxxxxxxx> > Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx> Reviewed-by: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx> Regards, Joonas _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
