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Re: [PATCH v2 0/3] Perf support to SDT markers
- From: Hemant <hkshaw at linux dot vnet dot ibm dot com>
- To: Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>
- 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
- Date: Tue, 08 Oct 2013 18:23:51 +0530
- Subject: Re: [PATCH v2 0/3] Perf support to SDT markers
- Authentication-results: sourceware.org; auth=none
- References: <20131007063911 dot 11693 dot 33624 dot stgit at hemant-fedora> <5253A04E dot 4020809 at hitachi dot com>
On 10/08/2013 11:33 AM, Masami Hiramatsu wrote:
Hi,
Hi Masami and thanks a lot for testing these patches.
(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.
Yes, I will rebase this series next time.
[...]
- 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.
OK, will include the binary name too.
$ ./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.
Yeah, correct.
$ ./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.
Yes, we can restrict action of --markers for -x option only. I thought
of keeping the same behavior as in case of function listing but I guess
restricting it would be better since, --markers should only be available
in user space.
- 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)
Ok, will rectify this behavior.
I'll review each patch soon.
Thanks, looking forward to that.
- Hemant