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

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Message-ID: <y0mbo2cs2oa.fsf@fche.csb>
Date:	Sat, 26 Oct 2013 07:16:05 -0400
From:	fche@...hat.com (Frank Ch. Eigler)
To:	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:

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.

- FChE
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