linux-kernel - Re: [PATCH v4 2/3] Support for perf to probe into SDT markers:

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Message-ID: <526E2304.1000407@iki.fi>
Date:	Mon, 28 Oct 2013 10:40:36 +0200
From:	Pekka Enberg <penberg@....fi>
To:	"Frank Ch. Eigler" <fche@...hat.com>,
	Pekka Enberg <penberg@...nel.org>
CC:	Hemant Kumar <hkshaw@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Oleg Nesterov <oleg@...hat.com>,
	hegdevasant@...ux.vnet.ibm.com, Ingo Molnar <mingo@...hat.com>,
	anton@...hat.com, systemtap@...rceware.org,
	Namhyung Kim <namhyung@...nel.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	aravinda@...ux.vnet.ibm.com
Subject: Re: [PATCH v4 2/3] Support for perf to probe into SDT markers:

On 10/26/2013 02:16 PM, Frank Ch. Eigler wrote:
> Pekka Enberg <penberg@...nel.org> writes:
>
>> Is there a technical reason why 'perf list' could not show all the
>> available SDT markers on a system and that the 'mark to event'
>> mapping cannot happen automatically? [...]
> A quick experiment with:
>
>    find `echo $PATH | tr : ' '` -type f -perm -555 |
>         xargs readelf -n 2>/dev/null |
>         grep STAP 2>/dev/null
>
> suggests reasonable performance for my F19 workstation (a second or
> two over ~6000 executables), once all the ELF content is in the block
> cache.  According to a stap eventcount.stp run, that required about
> 50000 syscall.read events.
>
> Note that a $PATH search excludes shared libraries, which can also
> carry <sys/sdt.h> markers.  Adding /usr/lib* in more than doubles the
> work, then there's /usr/libexec etc.

Thanks for providing numbers to the discussion. AFAICT, we
might even be able to just scan everything for 'perf list' by
default.

                     Pekka
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