From: Peter Zijlstra <peterz@infradead.org>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>,
Josh Poimboeuf <jpoimboe@redhat.com>,
linux-kernel@vger.kernel.org,
Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>,
Thomas Gleixner <tglx@linutronix.de>,
"H . Peter Anvin" <hpa@zytor.com>,
Andrey Konovalov <andreyknvl@google.com>,
Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH tip/master v3] kprobes: extable: Identify kprobes' insn-slots as kernel text area
Date: Wed, 4 Jan 2017 11:01:02 +0100 [thread overview]
Message-ID: <20170104100102.GE25813@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <20170104140604.5e2d53c69580f5c67ea6cd62@kernel.org>
On Wed, Jan 04, 2017 at 02:06:04PM +0900, Masami Hiramatsu wrote:
> On Tue, 3 Jan 2017 11:54:02 +0100
> Peter Zijlstra <peterz@infradead.org> wrote:
> > How many entries should one expect on that list? I spend quite a bit of
> > time reducing the cost of is_module_text_address() a while back and see
> > that both ftrace (which actually needs this to be fast) and now
> > kprobes have linear list walks in here.
>
> It depends on how many probes are used and optimized. However, in most
> cases, there should be one entry (unless user defines optimized probes
> over 32 on x86, from my experience, it is very rare case. :) )
OK, that's good :-)
> > I'm assuming the ftrace thing to be mostly empty, since I never saw it
> > on my benchmarks back then, but it is something Steve should look at I
> > suppose.
> >
> > Similarly, the changelog here should include some talk about worst case
> > costs.
>
> Would you have any good benchmark to measure it?
Not trivially so; what I did was cobble together a debugfs file that
measures the average of the PMI time in perf_sample_event_took(), and a
module that has a 10 deep callchain around a while(1) loop. Then perf
record with callchains for a few seconds.
Generating the callchain does the unwinder thing and ends up calling
is_kernel_address() lots.
The case I worked on was 0 modules vs 100+ modules in a distro build,
which was fairly obviously painful back then, since
is_module_text_address() used a linear lookup.
I'm not sure I still have all those bits, but I can dig around a bit if
you're interested.
next prev parent reply other threads:[~2017-01-04 10:01 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-22 6:42 Detecting kprobes generated code addresses Josh Poimboeuf
2016-12-25 3:13 ` Masami Hiramatsu
2016-12-25 6:16 ` Masami Hiramatsu
2016-12-26 4:30 ` Masami Hiramatsu
2016-12-26 14:50 ` [PATCH tip/master] kprobes: extable: Identify kprobes' insn-slots as kernel text area Masami Hiramatsu
2016-12-26 15:34 ` [PATCH tip/master v2] " Masami Hiramatsu
2016-12-26 17:21 ` kbuild test robot
2016-12-26 17:46 ` kbuild test robot
2016-12-27 6:13 ` Masami Hiramatsu
2016-12-27 6:14 ` [PATCH tip/master v3] " Masami Hiramatsu
2017-01-03 10:54 ` Peter Zijlstra
2017-01-04 5:06 ` Masami Hiramatsu
2017-01-04 10:01 ` Peter Zijlstra [this message]
2017-01-08 4:22 ` Masami Hiramatsu
2017-01-08 12:31 ` Masami Hiramatsu
2017-01-08 14:58 ` [PATCH tip/master v4] " Masami Hiramatsu
2017-01-09 17:36 ` Josh Poimboeuf
2017-01-10 1:11 ` Masami Hiramatsu
2017-01-10 8:59 ` Peter Zijlstra
2017-01-10 21:42 ` Josh Poimboeuf
2017-01-11 9:57 ` Masami Hiramatsu
2017-01-14 9:56 ` [tip:perf/core] kprobes, extable: Identify kprobes trampolines " tip-bot for Masami Hiramatsu
2017-01-04 14:21 ` [PATCH tip/master v3] kprobes: extable: Identify kprobes' insn-slots " Steven Rostedt
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