Messages in this thread | | | Subject | Re: [x86, sched] 2a0abc5969: phoronix-test-suite.stress-ng.SystemVMessagePassing.bogo_ops_s -14.1% regression | From | Giovanni Gherdovich <> | Date | Mon, 16 Nov 2020 10:31:25 +0100 |
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On Mon, 2020-11-16 at 15:07 +0800, kernel test robot wrote: > Greeting, > > FYI, we noticed a -14.1% regression of phoronix-test-suite.stress-ng.SystemVMessagePassing.bogo_ops_s due to commit: > > > commit: 2a0abc59699896f03bf6f16efb8a3a490511216f ("x86, sched: Add support for frequency invariance on SKYLAKE_X") > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master > > > in testcase: phoronix-test-suite > on test machine: 96 threads Intel(R) Xeon(R) Gold 6252 CPU @ 2.10GHz with 192G memory > with following parameters: > > test: stress-ng-1.2.2 > option_a: System V Message Passing > cpufreq_governor: performance > ucode: 0x5002f01
I haven't checked this regression yet, but when a "schedutil" change like this patch triggers a regression when the "performance" governor is used, the trouble might come in some roundabout way, eg. from cache alignment issues.
The patch defines a number of (not necessarily aligned) per-cpu variables, and there was a recent thread where Boris Petkov, Tony Luck and Mel Gorman debugged something that had similar characteristics:
"RE: [LKP] Re: [x86/mce] 1de08dccd3: will-it-scale.per_process_ops -14.1% regression" https://lore.kernel.org/lkml/6e996ad05e434a6fb13f069ee72b876b@intel.com/
I'll study this problem with that in mind.
Giovanni
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