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

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Date:	Sun, 20 Jul 2014 12:16:46 +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: Re: [PATCH v2 0/3] perf/sdt : Support for SDT markers

(2014/07/20 2:32), Hemant Kumar wrote:
>>> 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?
>>
> 
> I agree with you having perf sdt-cache similar to perf buildid-cache.
> But I think if the functionality of perf sdt-cache is only to build the 
> cache, then we can
> go with the perf list sdt --scan. Since, "perf list sdt" is used for 
> other purposes too, it
> should be less confusing for the users to just add another option 
> (--scan) to create/modify
> the cache. What do you suggest?

I think there may be some other cases, for example adding user local build
binary to the cache, or remove/update it locally. :)

And also, in user's mental model of perf-list, it doesn't take an "active"
action, that always does "passive" action. So adding such "active" scan option
will be more confusing.

But I also think it is OK that if the sdt is never scanned, the perf-list
automatically scans in background (without any option) or suggests user
to run "perf sdt-cache --scan". (it depends on how long time it may take)

To summarize it, I'd like to suggest adding below functions;

perf list sdt : shows all cached SDT events
perf list sdt <file> : shows SDT events in <file>
perf sdt-cache --scan/-s : scans all system binaries/libraries + added files
perf sdt-cache --add/-a <file(s)> : add SDT events in <file> to cache
perf sdt-cache --remove/-r <file(s)>: remove SDT events in <file> from cache

And if perf list can't find sdt-cache, it would suggest to run
perf sdt-cache --scan or run it silently. :)

What would you think about this?

Thank you,

-- 
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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