Setup: * SKL or KBL device (don't have data from others) * Ubuntu 18.04 / Unity * drm-tip v4.19 or newer kernel * git version of X with modifiers (dmabuf capable) enabled * Mesa git version Test-case: * multithreading --fullscreen --benchmark --benchwarmup 3 --benchruntime 20 Result: * FPS drops by 5-10% Between following Mesa commits: 41c8f991379d1a 2018-11-12 18:28:04 util: Fix warning in u_cpu_detect on non-x86 25b48e3df93dee 2018-11-14 12:12:09 st/xa: Bump minor Along with the perf drop, one can see both CPU & GPU power usage drops (according to RAPL), and GPU spending 30-40% in RC6 instead of 0%. I.e. there's a Mesa change that makes this GPU test CPU bound. I didn't see any significant perf changes in other benchmarks (Vulkan or GL).
There was some change between following commits: * 2018-12-31 19:52:08 8c93ef5de9: radv: Do a cache flush if needed before reading predicates. * 2019-01-02 18:09:04 7d6babf995: nir: add a way to print the deref chain That changed the multithreading test perf: * Fixed half of KBL-7 GT2 regression * Fixed half of combined perf regression for SKL-i5 GT2, for the indicated interval, and another (as large) regression at end of November * Improved perf a lot on BDW-3 GT2, much more than the small regression GPU still spends significant time in RC6 (~20% on BDW-i3, 35-40% on SKL-i5, 45% on KBL-i7). CPU vs GPU power usage changes differ between platforms, but they're fairly small. All in all, pretty nice with clearly increased perf.
In more detail: * BDW-i3 GT2 (256KB, 3MB LLC), BSW and BXT didn't regress originally, and improved clearly between commits indicated in above comment * There was no improvement on HSW-7 GT2 (1024KB, 8MB LLC), SKL-i7 GT4e (1024KB, 6MB LLC), KBL-i7 GT3e (512KB, 4MB LLC), and I don't have data on whether they regressed originally * Original regression was large on SKL-i5 GT2 (1024KB, 6MB LLC), SKL-i5 GT3e (512KB, 4MB LLC), KBL-i7 GT2 (512KB, 4MB LLC). SKL GT3e didn't improve, others did Current status for things on which I still have data that they had clearly regressed originally: * SKL & KBL GT2: 10-15% behind original perf * SKL GT3e: ~20% behind original perf There's some possible confusion here due to our build server and other changes happening at same time with v4.20-rc kernel STIBP mitigations. If somebody can confirm the regressions that would be nice. I'm fine with WONTFIX or WORKSFORME resolutions though, Vulkan multithreading isn't very interesting use-case (at least yet).
The i915 team has agreed that this is WONTFIX
verified.
Use of freedesktop.org services, including Bugzilla, is subject to our Code of Conduct. How we collect and use information is described in our Privacy Policy.