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

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Message-ID: <140ee1c060f22286fe2f4d81170f76be.squirrel@www.firstfloor.org>
Date:	Tue, 21 Sep 2010 19:36:00 +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

> On Tue, 2010-09-21 at 16:41 +0200, Andi Kleen wrote:
>> >
>> > So there are ~150 tracepoints, but this code is also being proposed
>> for
>> > use with 'dynamic debug' of which there are > 1000, and I'm hoping for
>> > more users moving forward.
>>
>> Even 1000 is fine to walk, but if it was sorted a binary search
>> would be much faster anyways. That is then you would still
>> need to search for each module, but that is a relatively small
>> number (< 100)
>
> xfs has > 100 tracepoints

Doesn
>
>>
>> > Also, I think the hash table deals nicely with modules.
>>
>> Maybe but it's also a lot of code. And it seems to me
>> that it is optimizing the wrong thing. Simpler is nicer.
>
> I guess simplicity is in the eye of the beholder. I find hashes easier
> to deal with than binary searching sorted lists. Every time you add a
> tracepoint, you need to resort the list.

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.

> Hashes are much easier to deal with and scale nicely. I don't think
> there's enough rational to switch this to a binary list.

Well problem is that the code is very complicated today. I suspect
this could be done much simpler if it wasn't so overengin

-Andi


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