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

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Date:	Thu, 19 Dec 2013 15:46:02 -0500
From:	fche@...hat.com (Frank Ch. Eigler)
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Ingo Molnar <mingo@...nel.org>, 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

Hi, Masami -

masami.hiramatsu.pt wrote:

> Here is the version 6 of NOKPROBE_SYMBOL series. :)
> [...]

Some preliminary results from building these on top of tip/master on
x86-64.  

# stap -te "probe kprobe.function("*") {}"

starts up OK, without crashes, which looks like great progress.  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'.  So, one
has to let the thing run for several hours just to get all the kprobes
inserted, never mind letting stress-testing begin.

For reference, here's the steady-state "perf top" output during all this
insertion work:

 54.81%  [kernel]                    [k] _raw_spin_unlock_irqrestore
 38.13%  [kernel]                    [k] __slab_alloc
  1.11%  [kernel]                    [k] kprobe_ftrace_handler
  0.88%  [kernel]                    [k] _raw_spin_unlock_irq

More notes once the machine gets far enough to get to the robustness
testing phase.

- FChE
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