Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   ebiederm@xmission.com (Eric W. Biederman)
To:     Alexey Gladkov <gladkov.alexey@gmail.com>
Cc:     kernel test robot <oliver.sang@intel.com>,
        0day robot <lkp@intel.com>,
        LKML <linux-kernel@vger.kernel.org>, lkp@lists.01.org,
        ying.huang@intel.com, feng.tang@intel.com, zhengjun.xing@intel.com,
        io-uring@vger.kernel.org,
        Kernel Hardening <kernel-hardening@lists.openwall.com>,
        Linux Containers <containers@lists.linux-foundation.org>,
        linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Jann Horn <jannh@google.com>, Jens Axboe <axboe@kernel.dk>,
        Kees Cook <keescook@chromium.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>
References: <20210224051845.GB6114@xsang-OptiPlex-9020>
        <m1czwpl83q.fsf@fess.ebiederm.org>
        <20210224183828.j6uut6sholeo2fzh@example.org>
Date:   Wed, 24 Feb 2021 12:50:21 -0600
In-Reply-To: <20210224183828.j6uut6sholeo2fzh@example.org> (Alexey Gladkov's
        message of "Wed, 24 Feb 2021 19:38:28 +0100")
Message-ID: <m17dmxl2qa.fsf@fess.ebiederm.org>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux)
MIME-Version: 1.0
Content-Type: text/plain
Subject: Re: d28296d248:  stress-ng.sigsegv.ops_per_sec -82.7% regression
Precedence: bulk

Alexey Gladkov <gladkov.alexey@gmail.com> writes:

> On Wed, Feb 24, 2021 at 10:54:17AM -0600, Eric W. Biederman wrote:
>> kernel test robot <oliver.sang@intel.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