netdev - Re: [PATCH] net: pfifo_fast - use ffs(x)-1 instead of array lookup

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Message-Id: <20120313.002559.340117447102423900.davem@davemloft.net>
Date:	Tue, 13 Mar 2012 00:25:59 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	zenczykowski@...il.com
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] net: pfifo_fast - use ffs(x)-1 instead of array lookup

From: Maciej Żenczykowski <zenczykowski@...il.com>
Date: Tue, 13 Mar 2012 00:23:27 -0700

> I was actually leaning towards going with ffs()-1, since
> 
> it's excellent on x86-64
> good on x86_cmov
> decent on x86
> good on armv5+
> 
> and I'm guessing it'll be good or better on any modern platform

Cycle count it with the pure integer operation variant, I bet it's
within a cycle or two, and at that point we're just splitting hairs
for an ugly-as-sin ifdef.
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