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Message-ID: <40dc40d5-58ff-e5b9-4e33-b0ce08ca0521@redhat.com> Date: Fri, 12 Apr 2019 12:43:03 -0400 From: Waiman Long <longman@...hat.com> To: kernel test robot <rong.a.chen@...el.com> Cc: Ingo Molnar <mingo@...nel.org>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Andrew Morton <akpm@...ux-foundation.org>, Davidlohr Bueso <dave@...olabs.net>, Linus Torvalds <torvalds@...ux-foundation.org>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de>, Tim Chen <tim.c.chen@...ux.intel.com>, Will Deacon <will.deacon@....com>, LKML <linux-kernel@...r.kernel.org>, "H. Peter Anvin" <hpa@...or.com>, tipbuild@...or.com, lkp@...org Subject: Re: [locking/rwsem] 1b94536f2d: stress-ng.bad-altstack.ops_per_sec -32.7% regression On 04/12/2019 10:20 AM, kernel test robot wrote: > Greeting, > > FYI, we noticed a -32.7% regression of stress-ng.bad-altstack.ops_per_sec due to commit: > > > commit: 1b94536f2debc98260fb17b44f7f262e3336f7e0 ("locking/rwsem: Implement lock handoff to prevent lock starvation") > https://git.kernel.org/cgit/linux/kernel/git/tip/tip.git WIP.locking/core > > in testcase: stress-ng > on test machine: 272 threads Intel(R) Xeon Phi(TM) CPU 7255 @ 1.10GHz with 112G memory > with following parameters: > > nr_threads: 100% > disk: 1HDD > testtime: 5s > class: memory > cpufreq_governor: performance > > > > > Details are as below: > --------------------------------------------------------------------------------------------------> > > > To reproduce: > > git clone https://github.com/intel/lkp-tests.git > cd lkp-tests > bin/lkp install job.yaml # job file is attached in this email > bin/lkp run job.yaml > > ========================================================================================= > class/compiler/cpufreq_governor/disk/kconfig/nr_threads/rootfs/tbox_group/testcase/testtime: > memory/gcc-7/performance/1HDD/x86_64-rhel-7.6/100%/debian-x86_64-2018-04-03.cgz/lkp-knm02/stress-ng/5s > > commit: > 1bcfe0e4cb ("locking/rwsem: Improve scalability via a new locking scheme") > 1b94536f2d ("locking/rwsem: Implement lock handoff to prevent lock starvation") > > 1bcfe0e4cb0efdba 1b94536f2debc98260fb17b44f7 > ---------------- --------------------------- > fail:runs %reproduction fail:runs > | | | > 1:4 -25% :4 dmesg.WARNING:at_ip__mutex_lock/0x > :4 25% 1:4 kmsg.DHCP/BOOTP:Reply_not_for_us_on_eth#,op[#]xid[#] > %stddev %change %stddev > \ | \ > 52766 ± 19% -32.8% 35434 ± 3% stress-ng.bad-altstack.ops > 10521 ± 19% -32.7% 7081 ± 3% stress-ng.bad-altstack.ops_per_sec > 71472 ± 16% -37.1% 44986 stress-ng.stackmmap.ops > 14281 ± 16% -37.0% 9001 stress-ng.stackmmap.ops_per_sec The lock handoff patch does have the side effect of reducing throughput for better fairness when there is extreme contention on a rwsem. I believe later patches that enable reader optimistic spinning should bring back some of the lost performance. Cheers, Longman
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