This is the mail archive of the
systemtap@sourceware.org
mailing list for the systemtap project.
Re: Performance Impact of Systemtap
- From: "Frank Ch. Eigler" <fche at redhat dot com>
- To: ydev <ydev at cs dot utah dot edu>
- Cc: systemtap at sourceware dot org
- Date: Fri, 9 Sep 2011 20:13:50 -0400
- Subject: Re: Performance Impact of Systemtap
- References: <cb5b1d6ea5cfb1a47de73cc67487972d@cs.utah.edu> <y0m4o0opgxj.fsf@fche.csb> <be418a6f9779e6bffd7c70c64777e8db@cs.utah.edu> <20110910001315.GA1560@redhat.com>
On Wed, Sep 07, 2011 at 08:42:23PM -0600, ydev wrote:
> Thank you Frank. I'm very new to SystemTap so could you please
> tell me what is the -DSTP_ALIBI mode run.
-DSTP_ALIBI compiles out the probe handlers from the systemtap module,
leaving only the parts that hook into the kernel, and just keep hit
counts/time. So it's as if the probe handlers were all { } empty.
> [...] I started systemtap in flight mode and triggered many
> reads/write and used the 'time' command to measure how long it takes
> to execute cat.
OK.
> I did this without systemtap running in the background. The figures
> were almost the same. I'm not sure if using 'time' command gives me
> accurate results.
Overall elapsed times should be accurate with /bin/time.
Instrumenting relatively few & slow calls like disk I/O should indeed
have negligible overhead when instrumented with systemtap.
- FChE