linux-kernel - Re: [PATCH v2 0/3] Perf support to SDT markers

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Message-ID: <5253A04E.4020809@hitachi.com>
Date:	Tue, 08 Oct 2013 15:03:58 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Hemant Kumar <hkshaw@...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
Subject: Re: [PATCH v2 0/3] Perf support to SDT markers

Hi,

(2013/10/07 15:46), Hemant Kumar wrote:
> This patchset helps in probing dtrace style markers(SDT) present in user space
> applications through perf. Notes/markes 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.

Thank you for updating!
By the way, could you rebase this series to the latest -tip kernel next time?
It is more convenient for us to test & merge it.

[...]
> - Now use perf to list the markers in the app:
> # perf probe --markers -x ./user_app
> 
> %user_app:foo_start
> %user_app:fun_start

Here, what I got.

$ ./perf probe --markers -x /lib64/librt.so
%librt:lll_futex_wake

OK, it lists up markers.

$ ./perf probe --markers -x ./perf
SDT markers not present!
  Error : Failed to find SDT markers!(-1)

OK, this shows an error, INHO, it'd better show which binary doesn't have markers.

$ ./perf probe --markers
Failed to open (null)
  Error : Failed to find SDT markers!(-1)

Hmm, it's a bit odd error. It should check if there is an elf binary is specified.

$ ./perf probe --markers /lib64/librt.so
%librt:lll_futex_wake

It seems to work without -x. However, that is only when the path is started with /.
And also the usage is not described by --help.

$ ./perf probe --markers ./perf
Semantic error :File always requires line number or lazy pattern.
  Error: Parse Error.  (-22)

So, to avoid confusion, --markers should abort without -x(--exec) option.

> - And  then use perf probe to add a probe point :
> 
> # perf probe -x ./user_app -a '%user_app:foo_start'

And also, without -x, -a also exits with an odd error message.

$ ./perf probe -a %libm:slowexp_p6
Failed to open (null)
  Error: Failed to add events. (-1)

I'll review each patch soon.

Thank you,

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

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