linux-kernel - Re: [PATCH v2 0/3] perf/sdt : Support for SDT markers

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Date:	Fri, 18 Jul 2014 20:23:35 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Hemant Kumar <hemant@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, srikar@...ux.vnet.ibm.com,
	peterz@...radead.org, oleg@...hat.com,
	hegdevasant@...ux.vnet.ibm.com, mingo@...hat.com, anton@...hat.com,
	systemtap@...rceware.org, namhyung@...nel.org,
	aravinda@...ux.vnet.ibm.com, penberg@....fi
Subject: Re: [PATCH v2 0/3] perf/sdt : Support for SDT markers

Hi Hemant,

(2014/07/17 14:53), Hemant Kumar wrote:
> This patchset helps in listing dtrace style markers(SDT) present in user space
> applications through perf.
> Notes/markers are placed at important places by the
> developers. They have a negligible overhead when not enabled.
> We can enable them and probe at these places and find some important information
> like the arguments' values, etc.

Thanks for your work! This actually helps us a lot :)

> We have lots of applications which use SDT markers today, like:
> Postgresql, MySql, Mozilla, Perl, Python, Java, Ruby, libvirt, QEMU, glib
> 
> To add SDT markers into user applications:
> We need to have this header sys/sdt.h present.
> sys/sdt.h used is version 3.
> If not present, install systemtap-sdt-devel package (for fedora-18).
> 
> Please refer to the Documentation patch to see how the SDT markers are added into
> a program.
> 
> With this patchset,
> - Use perf to list the markers in the app:
> # perf list sdt ./user_app
> 
> ./user_app :
> %user_app:foo_start
> %user_app:fun_start
> 
> - Also, we can see the SDT markers present in our system in the usual binaries.
> These usual binaries are libraries (dsos) listed by ldconfig --print-cache and some
> binaries present in PATH environment variable.
> 
> First, scan the binaries using :
> # perf list sdt --scan

At a glance, maybe we'd better have perf sdt-cache as like as perf buildid-cache
for manage sdt information. what would you think?


> 
> Creating a cache of SDT markers...
> perf sdt cache created!
>  Use : "perf list sdt"
>  to see the SDT markers
> 
> After the sdt cache file is created, use perf list to view the markers :
> # perf list sdt
> 
> %rtld : init_start
> %rtld : init_complete
> %rtld : map_failed
> %rtld : map_start
> %rtld : lll_futex_wake
> ...
> ...
> %libgcc : unwind
> %libvirt : rpc_server_client_auth_allow
> %libvirt : rpc_server_client_auth_fail
> %libvirt : rpc_server_client_auth_deny

Looks good :)
It seems very useful for perf users.

Thank you,

> Also, by using "perf list", we can view all the SDT markers as events along with all
> the other events present in the system.
> Alternatively, one can view the /var/cache/perf/perf-sdt.cache directly.
> 
> This link shows an example of marker probing with Systemtap:
> https://sourceware.org/systemtap/wiki/AddingUserSpaceProbingToApps
> 
> Also, this link provides important info regarding SDT notes:
> http://sourceware.org/systemtap/wiki/UserSpaceProbeImplementation
> 
> - Markers in binaries :
> These SDT markers are present in the ELF in the section named
> ".note.stapsdt".
> Here, the name of the marker, its provider, type, location, base
> address, semaphore address.
> We can retrieve these values using the members name_off and desc_off in
> Nhdr structure. If these are not enabled, they are present in the ELF as nop.
> 
> Changes since last series :
> - Made the changes as discussed with Masami and Namhyung.
> - Now, "perf list" will also display the SDT markers as events along with other events.
> - Made some optimazations.
> 
> TODO:
> - Add support to probe these SDT markers as if they are events.
> - Recognizing arguments and support to probe on them.
> ---
> 
> Hemant Kumar (3):
>       This patch enables perf to list the SDT markers present in a system. It looks
>       This patch enables perf to look for SDT markers in a single file.
>       This patch adds the required documentation for perf support to SDT markers.
> 
> 
>  tools/perf/Documentation/SDT-markers.txt |  123 +++++
>  tools/perf/Documentation/perf-list.txt   |    7 
>  tools/perf/Makefile.perf                 |    1 
>  tools/perf/builtin-list.c                |    6 
>  tools/perf/util/parse-events.h           |    3 
>  tools/perf/util/sdt.c                    |  778 ++++++++++++++++++++++++++++++
>  tools/perf/util/symbol-elf.c             |  229 +++++++++
>  tools/perf/util/symbol.h                 |   19 +
>  8 files changed, 1164 insertions(+), 2 deletions(-)
>  create mode 100644 tools/perf/Documentation/SDT-markers.txt
>  create mode 100644 tools/perf/util/sdt.c
> 


-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


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