This is the mail archive of the
systemtap@sourceware.org
mailing list for the systemtap project.
Re: [PATCH v4 0/3] perf/sdt : Support for SDT markers
- From: Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>
- To: Hemant Kumar <hemant at linux dot vnet dot ibm dot com>, acme at kernel dot org
- Cc: linux-kernel at vger dot kernel dot org, srikar at linux dot vnet dot ibm dot com, peterz at infradead dot org, oleg at redhat dot com, hegdevasant at linux dot vnet dot ibm dot com, mingo at redhat dot com, anton at redhat dot com, systemtap at sourceware dot org, namhyung at kernel dot org, aravinda at linux dot vnet dot ibm dot com, penberg at iki dot fi
- Date: Thu, 28 Aug 2014 20:19:55 +0900
- Subject: Re: [PATCH v4 0/3] perf/sdt : Support for SDT markers
- Authentication-results: sourceware.org; auth=none
- References: <20140827213745 dot 13454 dot 46266 dot stgit at hemant-fedora>
(2014/08/28 6:43), Hemant Kumar wrote:
> The v3 patchset had some spacing errors because of my editor messing up during
> sending the patches. Resending the patchset again.
> 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.
>
> 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 (3rd patch in this series) 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
>
> 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
>
> This patchset has undergone a lot of changes since it was first introduced.
> Hence, the patchset has now been subdivided for more simplicity and ease of
> review (thanks to the suggestion from Namhyung Kim). This contains the first 2
> of the 4 patches as suggested here:
> https://lkml.org/lkml/2014/7/20/284
BTW, does this series only contain list command support?
> - 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 :
> - Subdivided the previous patchset into 4 patches to make it easier to review
> as suggested by Namhyung Kim. (This set includes first two of the four patches)
> - Made the required changes and some optimizations suggested by Masami, Namhyung
> and Andi.
>
> TODO:
> - Listing SDT events present in most of the binaries present in a system.
> - Maintaining a cache of the SDT events for faster lookup.
> - Add support to probe these SDT markers and integrate with a previous patch
> (support to perf to probe SDT markers) posted in lkml.
> https://lkml.org/lkml/2013/10/23/10
OK, I think we can postpone sdt-cache command, but this should go with
probe-side improvements, because if perf-list shows sdt markers, users
will be misled that the perf already supports sdt events.
I'm OK if we hold this on a non-released branch on acme's tree. But it
shouldn't be pushed to upstream without probe-side improvements.
Arnaldo, would you think that works on your tree?
Thank you,
--
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com