linux-kernel - Re: [PATCH -tip v7 24/26] kprobes: Enlarge hash table to 4096 entries

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Message-ID: <530FBA99.3050504@hitachi.com>
Date:	Fri, 28 Feb 2014 07:22:17 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Sandeepa Prabhu <sandeepa.prabhu@...aro.org>,
	Frederic Weisbecker <fweisbec@...il.com>, x86@...nel.org,
	Steven Rostedt <rostedt@...dmis.org>, fche@...hat.com,
	mingo@...hat.com, systemtap@...rceware.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH -tip v7 24/26] kprobes: Enlarge hash table to 4096 entries

(2014/02/28 6:45), Andi Kleen wrote:
> Masami Hiramatsu <masami.hiramatsu.pt@...achi.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@...achi.com


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