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Re: [PATCH -tip v7 24/26] kprobes: Enlarge hash table to 4096 entries
- From: Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>
- To: Andi Kleen <andi at firstfloor dot org>
- Cc: linux-kernel at vger dot kernel dot org, Ingo Molnar <mingo at kernel dot org>, Ananth N Mavinakayanahalli <ananth at in dot ibm dot com>, Sandeepa Prabhu <sandeepa dot prabhu at linaro dot org>, Frederic Weisbecker <fweisbec at gmail dot com>, x86 at kernel dot org, Steven Rostedt <rostedt at goodmis dot org>, fche at redhat dot com, mingo at redhat dot com, systemtap at sourceware dot org, "H. Peter Anvin" <hpa at zytor dot com>, Thomas Gleixner <tglx at linutronix dot de>
- Date: Tue, 04 Mar 2014 10:54:42 +0900
- Subject: Re: [PATCH -tip v7 24/26] kprobes: Enlarge hash table to 4096 entries
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- References: <20140227073315 dot 20992 dot 6174 dot stgit at ltc230 dot yrl dot intra dot hitachi dot co dot jp> <20140227073414 dot 20992 dot 16882 dot stgit at ltc230 dot yrl dot intra dot hitachi dot co dot jp> <87y50wut4j dot fsf at tassilo dot jf dot intel dot com> <530FBA99 dot 3050504 at hitachi dot com> <53144C01 dot 60106 at hitachi dot com> <20140303172050 dot GZ22728 at two dot firstfloor dot org>
(2014/03/04 2:20), Andi Kleen wrote:
>> So, we can see the hash table larger than 2^9 (512 entries,
>> which consumes 4KB) has no performance improvement.
>> Would you think 4kB is still big for kprobes? :)
>
> 4KB should be fine. Thanks for evaluating.
>
Ah, I mistook. There are other tables(for kretprobes and locks)
enlarged by this change too. To minimize the memory impact,
I decided to decouple those tables, because the hash of the
kretprobe tables are calculated by the task structure,
whereas kprobe table's hash comes from the probed address.
This means that the kretprobe has a different scalability issue,
and should be solved by a different way.
Thank you,
--
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com