linux-kernel - Re: aio is unlikely

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Message-ID: <464E7409.6020505@garzik.org>
Date:	Fri, 18 May 2007 23:50:33 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Nick Piggin <nickpiggin@...oo.com.au>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Phillip Susi <psusi@....rr.com>,
	Alex Volkov <avcp-lkmail@....net>,
	'Linux Kernel Mailing List' <linux-kernel@...r.kernel.org>
Subject: Re: aio is unlikely

Nick Piggin wrote:
> Aside from using branch constructs or hints that help the predictor
> guess the right way... I think gcc will move unlikely paths right past
> the end of the "likely" fastpath, so it can increase code size and be
> somewhat suboptimal in terms of icache usage.

Thanks for the reminder.  GCC definitely does code movement.

ISTR the code movement might even be "extreme", once the unit-at-a-time 
support arrived, placing "cold" code at the end of the compiled module.

	Jeff


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