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

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Message-ID: <20100921194858.GB3024@one.firstfloor.org>
Date:	Tue, 21 Sep 2010 21:48:58 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Andi Kleen <andi@...stfloor.org>,
	Jason Baron <jbaron@...hat.com>, linux-kernel@...r.kernel.org,
	mingo@...e.hu, 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

> I agree with Steven, Peter and Jason: due to the large amount of
> tracepoints we can end up patching, we should keep the hash tables. This

I suspect when it's cache cold the hash tables will be actually slower.
As a general rule memory bloat = slow.

> code is very similar to what I have in the tracepoints already and in
> the immediate values. So this code is solid and has been tested over a
> large user base for quite some time already.

FWIW "We always did it this way" is not a good argument 
in engineering discussions.

> One change I would recommend is to use a separate memory pool to
> allocate the struct jump_label_entry, to favor better locality. I did
> not do it in tracepoints and markers because each entry have a variable
> length, but given that struct jump_label_entry seems to be fixed-size,
> then we should definitely go for a kmem_cache_alloc().

Yes even more complexity, great idea.

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only.
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