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

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Message-ID: <20140209143709.GA31608@gmail.com>
Date:	Sun, 9 Feb 2014 15:37:09 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
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


* Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> wrote:

> I guess the second reason is why the stap takes so long time to set 
> probes. stap tries to register kprobes without disabled flag, that 
> means we enables thousands of probes (overheads).
> 
> So the similar thing happens when we enables events as below;
> 
>   # for i in /sys/kernel/debug/tracing/events/kprobes/* ; do date; echo 1 > $i; done
>   Wed Jan 29 10:44:50 UTC 2014
>   ...
> 
> I tried it and canceled after 4 min passed. It enabled about 17k 
> events and slowed down my system very much(I almost got hang check 
> timer).

Ok, I guess that's the slowdown bug that Frank reported.

> I think we should have some performance statistics (hit count?) and 
> if it goes over a threshold, we should stop enabling other events.

That really feels like a hack. How about fixing the root cause? Does 
the enabling of all probes have to be so slow?

Thanks,

	Ingo
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