On Fri, May 05, 2017 at 05:13:58PM +0100, Tvrtko Ursulin wrote: > > On 05/05/2017 15:49, Ville Syrjälä wrote: > > On Fri, May 05, 2017 at 12:43:21PM +0100, Tvrtko Ursulin wrote: > >> From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx> > >> > >> It seems that the DMC likes to transition between the DC states > >> a lot when there are no connected displays (no active power > >> domains) during simple command submission. > > > > Is it trapping on some interrupt register accesses or what? And > > if so which registers are affected? > > It looks like GT IIR or something along those lines it but I couldn't > say with total confidence. <read DC counters> for i in `seq 1 100` ; do IGT_NO_FORCEWAKE=1 intel_reg read <whatever> ; done <read DC counters> Should be a pretty trivial to run that against the suspect registers. > It is just a guess. Firmware binary > definitely "mentions" those registers as can be seen by inspecting it > with a hex editor. > > The data I collected at least seems to present a correlation between the > batch frequency and DC state transition frequency: > > tgt DC irqs irqs/s irq batch/s DC/s DC/batch > submit transitions / > freq batch > ======================================================================== > 10000 20000 78300 7830.00 1.96 4000.00 2000.00 0.50 > 9901 14000 52855 7550.71 1.32 5714.29 2000.00 0.35 > 9524 13500 49100 7328.36 1.23 5970.15 2014.93 0.34 > 9091 13500 49200 7235.29 1.23 5882.35 1985.29 0.34 > 5000 16900 33290 3916.47 0.83 4705.88 1988.24 0.42 > 3333 27800 69550 4932.62 1.74 2836.88 1971.63 0.70 > 1667 57200 80200 2655.63 2.01 1324.50 1894.04 1.43 > 909 80000 80034 1482.11 2.00 740.74 1481.48 2.00 > 476 87000 80039 820.91 2.00 410.26 892.31 2.18 > 196 160000 80055 334.40 2.00 167.08 668.34 4.00 > > Submitted batches were ~100us long in all cases. So with low batch > frequency it looks pretty believable. For example when we have 167.08 > batches/s, we have 334.40 irq/s - which is double - as expected for > execlists. And we get again double that in terms of DC transitions per > second. Each irq is one GT IIR write from the GPU side, and another from > the CPU side. GPU doesn't actually write the IIRs. It's just latching stuff from the ISR. Whether the ISR edge or some higher level interrupt event actually causes the DMC to kick into action isn't clear at all. My original impressions was that it just traps the register accesses. -- Ville Syrjälä Intel OTC _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
