linux-kernel - Re: [PATCH -tip v6 00/22] kprobes: introduce NOKPROBE

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Date:	Tue, 24 Dec 2013 10:19:01 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	"Frank Ch. Eigler" <fche@...hat.com>, linux-arch@...r.kernel.org,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Sandeepa Prabhu <sandeepa.prabhu@...aro.org>, x86@...nel.org,
	lkml <linux-kernel@...r.kernel.org>,
	"Steven Rostedt (Red Hat)" <rostedt@...dmis.org>,
	systemtap@...rceware.org, "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH -tip v6 00/22] kprobes: introduce NOKPROBE_SYMBOL(), cleanup
 and fixes crash bugs

(2013/12/23 22:04), Ingo Molnar wrote:
> 
> * Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> wrote:
> 
>>> I can reproduce one weirdness, with just 13 probes added, 'perf probe 
>>> -l' [which should really be 'perf probe list'!] executes very slowly:
>>>
>>>  # perf stat --null --repeat 3 perf probe -l
>>>
>>>  Performance counter stats for 'perf probe -l' (3 runs):
>>>
>>>        0.763640098 seconds time elapsed                                          ( +-  1.61% )
>>>
>>> 0.7 seconds is ridiculously long.
>>
>> This comes from the perf-probe's internal issue. It tries to get 
>> actual lines and files by using debuginfo. I guess most of the time 
>> consumed when processing huge kernel debuginfo.
> 
> No, I don't have any debuginfo, I never use it.

Then it should be a performance bug. I need to take a look.

BTW, this is just a bug of perf probe, for example,

 # wc -l /sys/kernel/debug/tracing/kprobe_events
 3204 /sys/kernel/debug/tracing/kprobe_events

 # ./perf stat --null --repeat 3 cat /sys/kernel/debug/tracing/kprobe_events

  Performance counter stats for 'cat /sys/kernel/debug/tracing/kprobe_events' (3 runs):

       0.032075943 seconds time elapsed                                          ( +- 38.72% )

So even with 3204 probes, listing the kprobe events only takes 0.03 sec.

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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