linux-kernel - Re: [PATCH v3] audit: Turn off TIF_SYSCALL

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Date:	Tue, 18 Feb 2014 15:17:45 -0500
From:	Eric Paris <eparis@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	linux-audit@...hat.com, linux-kernel@...r.kernel.org,
	Andi Kleen <andi@...stfloor.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Steve Grubb <sgrubb@...hat.com>
Subject: Re: [PATCH v3] audit: Turn off TIF_SYSCALL_AUDIT when there are no
 rules

On Sat, 2014-02-08 at 13:06 -0800, Andy Lutomirski wrote:
> This toggles TIF_SYSCALL_AUDIT as needed when rules change instead
> of leaving it set whenever rules might be set in the future.  This
> reduces syscall latency from >60ns to closer to 40ns on my laptop.

Al also politely reminded me it might be wise to get some perf data
about where exactly we are spending out time.  I don't know squat about
perf, but Linus always tells me to do:

perf record -g -e cycles:pp -F 25000 $YOURTEST
perf report -s symbol

(the "-s symbol" is so that you don't get separate data for the
different processes that are part of the kernel build - you'll just
want "general kernel data"), and on one of the kernel symbols just
select it and do "Zoom into kernel DSO". You should see something like
this:

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