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Re: [PATCH -tip v6 00/22] kprobes: introduce NOKPROBE_SYMBOL(), cleanup and fixes crash bugs
- From: Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>
- To: Ingo Molnar <mingo at kernel dot org>
- 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: Fri, 20 Dec 2013 18:31:37 +0900
- 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>
(2013/12/20 17:20), Ingo Molnar wrote:
>
> * Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> wrote:
>
>>> But a closer look indicates that the insertion of kprobes is
>>> taking about three (!!) orders of magnitude longer than before, as
>>> judged by the rate of increase of 'wc -l
>>> /sys/kernel/debug/kprobes/list'.
>>
>> Right, because kprobes are not designed for thousands of probes.
>
> Then this needs to be fixed, because right now this bug is making it
> near impossible to properly test kprobes robustness.
>
> For example a hash table (hashed by probe address) could be used in
> addition to the list, to speed up basic operations.
kprobe itself is already using hlist (6bits hash table).
Maybe we'd better expand the table bits. However, the iteration
of the list on debugfs is just doing seq_printf()s. I'm not exactly
sure what Frank complaints about...
I recommend Frank to use perf record and perf annotation to clarify
which part caused that slow down.
Thank you,
--
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com