Quoting Rafael Antognolli (2018-01-26 17:58:29) > On Fri, Jan 26, 2018 at 09:55:58AM -0800, Rafael Antognolli wrote: > > On Fri, Jan 26, 2018 at 08:23:13AM +0000, Chris Wilson wrote: > > > Quoting Rafael Antognolli (2018-01-26 01:26:34) > > > > Write a PIPE_CONTROL with CS stall followed by 14 dwords of 0 in the > > > > indirect context wa bb. > > > > > > 14 MI_NOOPS following? That isn't what you wrote in the code, but the > > > > Agreed, sorry. The workarounds says: > > > > 0x7a000004 0x00100000 + 14 dwords of 0. I counted 6 dwords from > > gen8_emit_pipe_control() and figured "just 8 more to 14". I think I had > > it right on my first version of this patch, but... > > > > > main thing you haven't explained is why. A normal batch will already > > > have a flush in its setup, but more to the point would be the only > > > reason this is required is because of an implicit 3DSTATE inside the > > > context image on preemption. Right? Otherwise it seems to be a purely > > > userspace problem. > > > > This is the text from the workaround: > > > > "This bug can be hit on a context restore. To avoid the issue the > > following must be programmed by SW to ensure the engine is idle prior to > > programming 3DSTATE_SAMPLE_PATTERN: > > > > With RS context enabled: 0x21c8 = 0x000085c0 > > > > With RS context disabled:0x21c8 = 0x00001ac0 > > > > The above program specifes the offset to insert driver programmed > > commands > > > > 0x21c4[31:6] = 0x<Addresses> > > > > 0x21c4[5:0] = 0x<N> > > > > N=Size of CL needed to fit Workaround > > > > The above programming is the GGTT address of the driver programmed > > commands and the size(# of CL) to execute. > > > > The address above needs to be a GGTT address and contain a pipe control > > with CS stall(0x7a000004 0x00100000 0x00000000 0x00000000)followed by > > 12DW’s of NOOP(0x00000000)" > > > > Since it needs to be in a GGTT address, and it's specifically talking > > about the Indirect Context Pointer, we figured it should be in the > > kernel. I can update the commit message with the above text if it helps. > > > > I originally implemented this trying to fix my GPU hang, but it turns > > out the issue was something else and this commit doesn't help at all. > > Still, I see no reason to not have it there just in case it prevent any > > future hangs... > > Oh, and this workaround is actually a little longer, and there is a part > that describe a similar PIPE_CONTROL before 3DSTATE_SAMPLE_PATTERN. That > part is already implemented in userspace.
Cool, I really just wanted confirmation that it was indeed required before the context switch. Hence justifying placement in the indirect_ctx bb, and explaining why it's not just a regular pre-batch flush. Please do try and distill as much as the workaround note into the changelog and a reminder inside the code; especially the rationale on why it's in the indirect ctx bb. -Chris _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx
