From: Waiman Long <longman@redhat.com>
To: kernel test robot <rong.a.chen@intel.com>
Cc: Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Borislav Petkov <bp@alien8.de>,
Davidlohr Bueso <dave@stgolabs.net>,
"H. Peter Anvin" <hpa@zytor.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
Tim Chen <tim.c.chen@linux.intel.com>,
Will Deacon <will.deacon@arm.com>,
huang ying <huang.ying.caritas@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
tipbuild@zytor.com, lkp@01.org
Subject: Re: [locking/rwsem] 4f23dbc1e6: reaim.jobs_per_min -37.0% regression
Date: Mon, 24 Jun 2019 15:45:03 -0400 [thread overview]
Message-ID: <f0381605-e266-4816-653a-91c6e17ca3a5@redhat.com> (raw)
In-Reply-To: <20190624054511.GA7221@shao2-debian>
On 6/24/19 1:45 AM, kernel test robot wrote:
> Greeting,
>
> FYI, we noticed a -37.0% regression of reaim.jobs_per_min due to commit:
>
>
> commit: 4f23dbc1e657951e5d94c60369bc1db065961fb3 ("locking/rwsem: Implement lock handoff to prevent lock starvation")
> https://git.kernel.org/cgit/linux/kernel/git/tip/tip.git locking/core
>
> in testcase: reaim
> on test machine: 48 threads Intel(R) Xeon(R) CPU E5-2697 v2 @ 2.70GHz with 64G memory
> with following parameters:
>
> runtime: 300s
> nr_task: 7000t
> test: shared_memory
> cpufreq_governor: performance
> ucode: 0x42e
>
> test-description: REAIM is an updated and improved version of AIM 7 benchmark.
> test-url: https://sourceforge.net/projects/re-aim-7/
With 7000 users, there will be extreme contention on the rwsems. The
lock handoff patch is known to reduce throughput with such level of lock
contention. This is a tradeoff between throughput and fairness. I don't
think this is a problem unless some real world workloads also have
significant regression in performance. I will try to reproduce the
regression and see if we can do something to reduce the performance
regression.
Cheers,
Longman
prev parent reply other threads:[~2019-06-24 19:45 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-24 5:45 [locking/rwsem] 4f23dbc1e6: reaim.jobs_per_min -37.0% regression kernel test robot
2019-06-24 19:45 ` Waiman Long [this message]
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