<html> <head> <base href="https://bugs.freedesktop.org/"> </head> <body> <div> <a class="bz_bug_link bz_status_NEW " title="NEW - [SKL dmc] Headless mode media transcoding is 20-30% slower comparing to connected monitor use case" href="https://bugs.freedesktop.org/show_bug.cgi?id=100572#c10">Comment # 10</a> on <a class="bz_bug_link bz_status_NEW " title="NEW - [SKL dmc] Headless mode media transcoding is 20-30% slower comparing to connected monitor use case" href="https://bugs.freedesktop.org/show_bug.cgi?id=100572">bug 100572</a> from <a class="email" href="mailto:tvrtko.ursulin@linux.intel.com" title="Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>"> Tvrtko Ursulin</a> <pre>(In reply to Tvrtko Ursulin from <a href="show_bug.cgi?id=100572#c9">comment #9</a>) > (In reply to Imre Deak from <a href="show_bug.cgi?id=100572#c7">comment #7</a>) > > (In reply to Tvrtko Ursulin from <a href="show_bug.cgi?id=100572#c6">comment #6</a>) > > > I tried not loading the DMC firmware and can confirm that the issue is not > > > present in that case. > > > > > > Also, it is possible to reproduce this in the default kernel config (no > > > pinning is required) simply with igt/benchmarks/gem_latency -n 0 in which > > > case the perf difference between the two setups was ~8x in my testing. > > > > One possibility is that DC6 enables deeper system level power states and > > this causes latency elsewhere. What are the PC state residencies shown by > > powertop or the kernel's tools/power/x86/turbostat when DMC is loaded and > > not? > > 1. With DMC, idle system, no displays: > > PKG is in PC2, CPU is in C7, GPU is in RC6. > > When looking in i915_dmc_info I can see that the "DC3 - > DC5" transition > counter increases exactly by one each second. "DC5 -> DC6 counter is zero". > > If I now run gem_latency -n 0: > > "DC3 -> DC5" counter starts increasing by ~2k per second. > > PKG is not any deeper states now. "not in" ! > CPU split between C2/C3/C6/C7 is approx. 42/2/10/40%. > GPU is 0% RC6. > > Benchmark goes slow. > > 2. Now I force turn on a display (echo on | > tee /sys/class/drm/card0-HDMI-A-1/status). > > "DC3 -> DC5" transition counter stops increasing. > > PKG is still in PC2, CPU in C7 and GPU in RC6. > > Benchmark is not normal speed and while it is running PKG is not in any low s/not/now/ :( So it is normal speed now! > power states, RC6 is 0% and CPU C2/C3/C6/C7 is approx 52/0/0/25%. > > 3. DMC not loaded, idle system, no displays > > PKG is now in PC7 (not PC2 as above!), CPU is C7, GPU is RC6. > > gem_latency is now normal speed with power states like above. > > Out of curiosity I tried forcing the display on in this config. That makes > the PKG go to ~3% PC2, rest in PC7. Turning it off again brings it back to > <0.5% PC2 and the rest in PC7. > > > What's the effect of limiting max_cstates to 0 (and having DMC loaded)? > > No effect on benchmark speed or reported "DC3 -> DC5" transitions. > > > An other problem could be that the GPU is trying to access the display, > > (maybe checking scan line counts or something?). > > You mean something behind the covers or explicitly by i915? > > > Does /sys/kernel/debug/dri/0/i915_dmc_info show any transitions during the > > test when DMC is loaded? > > Yes, see above. :)</pre> </div> <hr> You are receiving this mail because: <ul> <li>You are on the CC list for the bug.</li> <li>You are the assignee for the bug.</li> <li>You are the QA Contact for the bug.</li> </ul> </body> </html>