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Message-ID: <m17dmxl2qa.fsf@fess.ebiederm.org>
Date: Wed, 24 Feb 2021 12:50:21 -0600
From: ebiederm@...ssion.com (Eric W. Biederman)
To: Alexey Gladkov <gladkov.alexey@...il.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
Alexey Gladkov <gladkov.alexey@...il.com> writes:
> 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.
Which given the hickups with getting a working version seems justified.
Now we can add incremental patches on top to improve the performance.
Eric
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