linux-kernel - Re: [PATCH 03/10] jump label v11: base patch

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Date:	Tue, 21 Sep 2010 20:48:28 +0200
From:	"Andi Kleen" <andi@...stfloor.org>
To:	"Steven Rostedt" <rostedt@...dmis.org>
Cc:	"Andi Kleen" <andi@...stfloor.org>,
	"Jason Baron" <jbaron@...hat.com>, linux-kernel@...r.kernel.org,
	mingo@...e.hu, mathieu.desnoyers@...ymtl.ca, hpa@...or.com,
	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
Subject: Re: [PATCH 03/10] jump label v11: base patch

>> Doesn
>
> I suppose you were missing a 't'.

Sorry sentence was eaten (I had to type it twice because the webmail
thingy eat it first try and probably didn't finish
it second time). I did not doubt your trace point number :)

What I meant is that the number of trace points does not really
matter much for binary search, unless you're going to gigantic numbers.
100 is still searched in only a few tries.

What matters is just how many tables you need to walk and that
only scales with the number of modules, not the number of trace points.

for ( each module )
    binary search in section

Advantage: no additional memory, no setup code other than a simple
sort, less code overall.

Also most modules are small so a binary search try is likely very
fast.

The methology is also long proven for *_user() exception handling
and always worked well here.

>> The only time you add one is when you load a module, right? When you do
>> that you only sort the section of the new module.
>
> And on removing a module.

On removing you simply free the module table, no real work to do.

> Perhaps it can be cleaned up. But I have no issues with it now, and
> using a hash (basic data structures 101) is not where the complexity
> comes in.

Hash tables are not complex in themselves, but all the code to
maintain them still adds up. I think considerable parts of the
new code were simply that. IMHO that can be done simpler
at no real loss of functionality or performance.

-Andi

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