linux-kernel - Re: [PATCH 6/6] uprobes/perf: Always increment trace

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Date:	Mon, 4 Feb 2013 21:56:11 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Anton Arapov <anton@...hat.com>,
	Frank Eigler <fche@...hat.com>,
	Josh Stone <jistone@...hat.com>,
	"Suzuki K. Poulose" <suzuki@...ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/6] uprobes/perf: Always increment trace_uprobe->nhit

* Oleg Nesterov <oleg@...hat.com> [2013-02-04 16:18:50]:

> On 02/04, Srikar Dronamraju wrote:
> >
> > * Oleg Nesterov <oleg@...hat.com> [2013-01-31 20:18:32]:
> >
> > > Move tu->nhit++ from uprobe_trace_func() to uprobe_dispatcher().
> > >
> > > ->nhit counts how many time we hit the breakpoint inserted by this
> > > uprobe, we do not want to loose this info if uprobe was enabled by
> > > sys_perf_event_open().
> > >
> >
> > Though I dont see a problem with this change, It seems unnecessary for
> > me.
> >
> > Info from nhits is mostly for /sys/kernel/debug/tracing/uprobe_profile
> 
> It is only for uprobe_profile, yes, and it is useful. Why should we hide
> this info if this uprobe is used by perf?

Fine with me.

Steve, Masami, Do you have comments/suggestions on this. 
(Since kprobe_profile just accounts for kprobetracer and doesnt account
for perf record.)
May we should make a similar change in kprobetracer to keep things
similar.

-- 
Thanks and Regards
Srikar Dronamraju

> 
> > I am not sure how sys_perf_event_open() is making use of this?
> 
> I hope I'll send the final series today. From the changelog of the patch
> which actually turns the filtering on:
> 
> 	Testing:
> 
> 		# perf probe -x /lib/libc.so.6 syscall
> 
> 		# perl -e 'syscall -1 while 1' &
> 		[1] 530
> 
> 		# perf record -e probe_libc:syscall perl -e 'syscall -1 for 1..10; sleep 1'
> 
> 		# perf report --show-total-period
> 			100.00%            10     perl  libc-2.8.so    [.] syscall
> 
> 	Before this patch:
> 
> 		# cat /sys/kernel/debug/tracing/uprobe_profile
> 			/lib/libc.so.6 syscall				79291
> 
> 	A huge ->nrhit == 79291 reflects the fact that the background process
> 	530 constantly hits this breakpoint too, even if doesn't contribute to
> 	the output.
> 
> 	After the patch:
> 
> 		# cat /sys/kernel/debug/tracing/uprobe_profile
> 			/lib/libc.so.6 syscall				10
> 
> 	This shows that only the target process was punished by int3.
> 
> Oleg.
> 
> --
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