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Re: [PATCH -tip v6 00/22] kprobes: introduce NOKPROBE_SYMBOL(), cleanup and fixes crash bugs
- From: Ingo Molnar <mingo at kernel dot org>
- To: Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>
- Cc: "Frank Ch. Eigler" <fche at redhat dot com>, linux-arch at vger dot kernel dot org, Ananth N Mavinakayanahalli <ananth at in dot ibm dot com>, Sandeepa Prabhu <sandeepa dot prabhu at linaro dot org>, x86 at kernel dot org, lkml <linux-kernel at vger dot kernel dot org>, "Steven Rostedt (Red Hat)" <rostedt at goodmis dot org>, systemtap at sourceware dot org, "David S. Miller" <davem at davemloft dot net>
- Date: Sun, 9 Feb 2014 15:37:09 +0100
- Subject: Re: [PATCH -tip v6 00/22] kprobes: introduce NOKPROBE_SYMBOL(), cleanup and fixes crash bugs
- Authentication-results: sourceware.org; auth=none
- References: <20131219090353 dot 14309 dot 15496 dot stgit at kbuild-fedora dot novalocal> <y0m38loefhx dot fsf at fche dot csb> <52B3C5E6 dot 2040802 at hitachi dot com> <20131220082056 dot GA15934 at gmail dot com> <52B40E79 dot 8040701 at hitachi dot com> <20131220104615 dot GA22609 at gmail dot com> <52E8E487 dot 2090007 at hitachi dot com>
* Masami Hiramatsu <masami.hiramatsu.pt@hitachi.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