Date: Fri, 17 Sep 2004 21:58:42 +1000
From: Anton Blanchard <anton@samba.org>
To: Chris Friesen <cfriesen@nortelnetworks.com>
Cc: Andrew Morton <akpm@osdl.org>, Stelian Pop <stelian@popies.net>,
       linux-kernel@vger.kernel.org
Subject: Re: [RFC, 2.6] a simple FIFO implementation
Message-ID: <20040917115842.GJ2825@krispykreme>
References: <16714.14118.212946.499226@wombat.chubb.wattle.id.au> <414A7A01.9080708@nortelnetworks.com>
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> I did a similar test once for ppc that found that an increment followed by 
> a test (marked unlikely) was actually quicker in practice than modulo 
> arithmetic. The branch predictor got it right most of the time, so the 
>  test was almost free.

Yep x % y where y isnt constant could result in a divide which will blow
away 60+ cycles on some ppc machines. You can do a whole lot in those 60
cycles. Many memcpys for example :)

We removed all modulo arithmetic in the e1000 driver (replaced it with
if (x > y) x = 0) and managed to measure an improvement. 

Anton
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