lkml.org 
[lkml]   [2011]   [Nov]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [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@redhat.com>

Thanks,

-Jason


\
 
 \ /
  Last update: 2011-11-28 18:17    [W:0.055 / U:0.056 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site