Message-ID: <530FBA99.3050504@hitachi.com>
Date: Fri, 28 Feb 2014 07:22:17 +0900
From: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Organization: Hitachi, Ltd., Japan
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To: Andi Kleen <andi@firstfloor.org>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
        Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
        Sandeepa Prabhu <sandeepa.prabhu@linaro.org>,
        Frederic Weisbecker <fweisbec@gmail.com>, x86@kernel.org,
        Steven Rostedt <rostedt@goodmis.org>, fche@redhat.com,
        mingo@redhat.com, systemtap@sourceware.org,
        "H. Peter Anvin" <hpa@zytor.com>, Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH -tip v7 24/26] kprobes: Enlarge hash table to 4096 entries
References: <20140227073315.20992.6174.stgit@ltc230.yrl.intra.hitachi.co.jp> <20140227073414.20992.16882.stgit@ltc230.yrl.intra.hitachi.co.jp> <87y50wut4j.fsf@tassilo.jf.intel.com>
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(2014/02/28 6:45), Andi Kleen wrote:
> Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> writes:
> 
>> Currently, since the kprobes expects to be used
>> with less than 100 probe points, its hash table
>> just has 64 entries. This is too little to handle
>> several thousands of probes.
>> Enlarge this to 4096 entires which just consumes
>> 32KB (on 64bit arch) for better scalability.
> 
> 32K for a debug feature that most systems never use seems
> too large to me.
> 
> First can you check if smaller hash tables work too
> (perhaps with a better hash, like jhash) 

I doubt jhash helps it, but yes, at least the various size
should be tested.

> And then if you enlarge the table please allocate
> it dynamically on the first use.

OK, I'll try to do so.

Thank you,

-- 
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com


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