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Date: Wed, 24 Feb 2021 19:38:28 +0100
From: Alexey Gladkov <gladkov.alexey@...il.com>
To: "Eric W. Biederman" <ebiederm@...ssion.com>
Cc: kernel test robot <oliver.sang@...el.com>, 0day robot <lkp@...el.com>,
LKML <linux-kernel@...r.kernel.org>, lkp@...ts.01.org,
ying.huang@...el.com, feng.tang@...el.com, zhengjun.xing@...el.com,
io-uring@...r.kernel.org,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Linux Containers <containers@...ts.linux-foundation.org>,
linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
Christian Brauner <christian.brauner@...ntu.com>,
Jann Horn <jannh@...gle.com>, Jens Axboe <axboe@...nel.dk>,
Kees Cook <keescook@...omium.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Oleg Nesterov <oleg@...hat.com>
Subject: Re: d28296d248: stress-ng.sigsegv.ops_per_sec -82.7% regression
On Wed, Feb 24, 2021 at 10:54:17AM -0600, Eric W. Biederman wrote:
> kernel test robot <oliver.sang@...el.com> writes:
>
> > Greeting,
> >
> > FYI, we noticed a -82.7% regression of stress-ng.sigsegv.ops_per_sec due to commit:
> >
> >
> > commit: d28296d2484fa11e94dff65e93eb25802a443d47 ("[PATCH v7 5/7] Reimplement RLIMIT_SIGPENDING on top of ucounts")
> > url: https://github.com/0day-ci/linux/commits/Alexey-Gladkov/Count-rlimits-in-each-user-namespace/20210222-175836
> > base: https://git.kernel.org/cgit/linux/kernel/git/shuah/linux-kselftest.git next
> >
> > in testcase: stress-ng
> > on test machine: 48 threads Intel(R) Xeon(R) CPU E5-2697 v2 @ 2.70GHz with 112G memory
> > with following parameters:
> >
> > nr_threads: 100%
> > disk: 1HDD
> > testtime: 60s
> > class: interrupt
> > test: sigsegv
> > cpufreq_governor: performance
> > ucode: 0x42e
> >
> >
> > In addition to that, the commit also has significant impact on the
> > following tests:
>
> Thank you. Now we have a sense of where we need to test the performance
> of these changes carefully.
One of the reasons for this is that I rolled back the patch that changed
the ucounts.count type to atomic_t. Now get_ucounts() is forced to use a
spin_lock to increase the reference count.
--
Rgrds, legion
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