linux-kernel - Re: [PATCH] perf, core: rate limit perf_sched_events jump

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Message-ID: <20111128171445.GA2519@redhat.com>
Date:	Mon, 28 Nov 2011 12:14:45 -0500
From:	Jason Baron <jbaron@...hat.com>
To:	Gleb Natapov <gleb@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, mingo@...e.hu,
	rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] perf, core: rate limit perf_sched_events jump_label
 patching

On Sun, Nov 27, 2011 at 05:59:09PM +0200, Gleb Natapov wrote:
> jump_lable patching is very expensive operation that involves pausing all
> cpus. The patching of perf_sched_events jump_label is easily controllable
> from userspace by unprivileged user. When user runs loop like this
> "while true; do perf stat -e cycles true; done" the performance of my
> test application that just increments a counter for one second drops by
> 4%. This is on a 16 cpu box with my test application using only one of
> them. An impact on a real server doing real work will be much worse.
> Performance of KVM PMU drops nearly 50% due to jump_lable for "perf
> record" since KVM PMU implementation creates and destroys perf event
> frequently.
> 
> This patch introduce the way to rate limit jump_label patching and uses
> it to fix above problem. I believe that as jump_label use will spread
> the problem will become more common and thus solving it in a generic
> code is appropriate. Also fixing it in a perf code will result in moving
> jump_label accounting logic to perf code with all the ifdefs in case
> of JUMP_LABEL=n kernel. With this patch all details are nicely hidden
> inside jump_label code.
> 

Looks good to me.

Acked-by: Jason Baron <jbaron@...hat.com>

Thanks,

-Jason
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