linux-kernel - Re: [PATCH v2] signals: Avoid unnecessary taking of sighand->siglock

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Date:   Mon, 26 Sep 2016 17:24:36 -0400
From:   Waiman Long <waiman.long@....com>
To:     Stas Sergeev <stsp@...t.ru>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        <linux-kernel@...r.kernel.org>,
        Scott J Norton <scott.norton@....com>,
        Douglas Hatch <doug.hatch@....com>
Subject: Re: [PATCH v2] signals: Avoid unnecessary taking of sighand->siglock

On 09/23/2016 03:43 PM, Stas Sergeev wrote:
> 23.09.2016 19:56, Waiman Long пишет:
>> When running certain database workload on a high-end system with many
>> CPUs, it was found that spinlock contention in the sigprocmask syscalls
>> became a significant portion of the overall CPU cycles as shown below.
> Hi, I was recently facing the same problem, and my solution
> was to extract swapcontext() from libtask - it has better semantic
> and does not do sigprocmask. How much you hack sigprocmask,
> it is still faster to just not call it at all.
> Alternatively, perhaps the speed-up can be achieved if the
> current mask is exported to glibc via vdso.
> Just my 2 cents.

The problem was in a third-party software not under our control. I am 
just doing my part to try to alleviate the problem from the kernel's 
perspective.

Cheers,
Longman