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Re: [PATCH v4 2/3] Support for perf to probe into SDT markers:
- From: Pekka Enberg <penberg at iki dot fi>
- To: David Ahern <dsahern at gmail dot com>, Srikar Dronamraju <srikar at linux dot vnet dot ibm dot com>
- Cc: Hemant Kumar <hkshaw at linux dot vnet dot ibm dot com>, LKML <linux-kernel at vger dot kernel dot org>, Peter Zijlstra <peterz at infradead dot org>, Oleg Nesterov <oleg at redhat dot com>, "hegdevasant at linux dot vnet dot ibm dot com" <hegdevasant at linux dot vnet dot ibm dot com>, Ingo Molnar <mingo at redhat dot com>, "anton at redhat dot com" <anton at redhat dot com>, "systemtap at sourceware dot org" <systemtap at sourceware dot org>, Namhyung Kim <namhyung at kernel dot org>, Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>, "aravinda at linux dot vnet dot ibm dot com" <aravinda at linux dot vnet dot ibm dot com>
- Date: Mon, 28 Oct 2013 10:48:42 +0200
- Subject: Re: [PATCH v4 2/3] Support for perf to probe into SDT markers:
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Hi David,
On 10/25/2013 06:20 PM, David Ahern wrote:
On 10/25/13 8:20 AM, Pekka Enberg wrote:
Technically feasible. But then we would have to parse each of the
libraries and executables to list them. Right? I am not sure if such a
delay is acceptable.
You could do it at 'perf list' time or even build time and cache it.
And add lazy discovery to 'perf record' and friends.
Instead searching all the known files or building a cache, how about
just having an option like: perf list <DSO>. perf-record could still
do the probe magic behind the scenes.
We probably should also support that. But I don't see why
'perf list' could not tell me about SDT markers in libraries that
are already installed on my system.
The problem I have with all the command line magic is that
while the tracing mechanisms are awesome, they're nearly
impossible to discover even by a power user such as myself
and you almost certainly forget the exact syntax over time.
It's not as if you're tracing all the time.
I wish people remembed how awesome and simple 'perf stat'
and 'perf record' with 'perf report' were compared to oprofile
when the first versions came out. I think much of the nice
perf features are suffering because we're not paying enough
attention how to make them accessible to users.
The proposed SDT marker feature is a good example of that.
I mean, how on earth would I know about the userspace
probes unless I read LKML and know that such a feature
exists? And why would I want to provide mappings for SDT
markers and perf events if I want to trace 'libc:setjmp'?
So I really hope this SDT effort and the ktap effort at least
make some effort in unifying all the nice functionality that's
simple to use and easy to discover. I really, really would
at the end of the day, just 'perf trace' like I 'perf stat' or
'perf record'.
Pekka