linux-kernel - Re: [PATCH 2/2] Rewrite jump_label.c to use binary search

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Message-ID: <4C9A61AE.3080804@zytor.com>
Date:	Wed, 22 Sep 2010 13:06:06 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC:	Andi Kleen <andi@...stfloor.org>, jbaron@...hat.com,
	rostedt@...dmis.com, linux-kernel@...r.kernel.org, mingo@...e.hu,
	tglx@...utronix.de, roland@...hat.com, rth@...hat.com,
	mhiramat@...hat.com, fweisbec@...il.com, avi@...hat.com,
	davem@...emloft.net, vgoyal@...hat.com, sam@...nborg.org,
	tony@...eyournoodle.com, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 2/2] Rewrite jump_label.c to use binary search

On 09/22/2010 12:43 PM, Mathieu Desnoyers wrote:
> * H. Peter Anvin (hpa@...or.com) wrote:
>> On 09/22/2010 03:08 AM, Andi Kleen wrote:
> 
> That's a very interesting idea, which applies very well to exception
> handlers, but tracepoints and static jumps suffer from the problem that
> there are many possible instances of the same key.
> 
> Tracepoints use a lookup by tracepoint name. Static jumps use a lookup
> by associated variable address (but this variable can be associated with
> many instances, e.g. in the case of static inline functions, or just
> when the same variable is used to control many instances of static
> jumps).
> 
> But maybe we could find a way to do an initial sort phase, so the
> perfect hash could point to the first entry corresponding to the looked
> up key ?
> 

In the case of multiple instances of the same key you want the perfect
hash to point to the cluster of solutions -- a list.  Since this is by
necessity something that needs to be done at compile time that list can
simply be an array.

	-hpa
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