|Summary:||~10% perf drop in Sascha Willems Vulkan Multithreading demo|
|Product:||Mesa||Reporter:||Eero Tamminen <eero.t.tamminen>|
|Component:||Drivers/Vulkan/intel||Assignee:||Intel 3D Bugs Mailing List <intel-3d-bugs>|
|Status:||VERIFIED WONTFIX||QA Contact:||Intel 3D Bugs Mailing List <intel-3d-bugs>|
|i915 platform:||i915 features:|
|Bug Depends on:|
Description Eero Tamminen 2018-12-13 18:06:58 UTC
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).
Comment 1 Eero Tamminen 2019-01-11 15:32:20 UTC
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.
Comment 2 Eero Tamminen 2019-02-06 11:58:02 UTC
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).
Comment 3 Mark Janes 2019-02-28 17:15:28 UTC
The i915 team has agreed that this is WONTFIX
Comment 4 Eero Tamminen 2019-03-01 08:47:16 UTC