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Re: [PATCH -tip v6 00/22] kprobes: introduce NOKPROBE_SYMBOL(), cleanup and fixes crash bugs
- From: "Frank Ch. Eigler" <fche at redhat dot com>
- To: Ingo Molnar <mingo at kernel dot org>
- Cc: Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi 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 16:27:24 -0500
- 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> <20140209143709 dot GA31608 at gmail dot com>
Hi -
> > 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.
It could be, but it feels a bit different. In my testing from
December, it's as though it wasn't the activated probes *hitting* that
were associated with the slowdown, but them merely being activated.
It was as though something with the kprobes/ftrace probe-registration
code performed a lot more work than it did longer ago. (One way to
test this could be to be more careful in the selection of kprobes
being enabled. For examle, emplace thousands, but only unused loaded
modules.) I'm sorry I didn't get time to investigate further.
- FChE