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Re: 3c59x

To: Jeff Garzik <jgarzik@xxxxxxxxx>
Subject: Re: 3c59x
From: Andi Kleen <ak@xxxxxxx>
Date: Tue, 10 Jun 2003 19:18:16 +0200
Cc: "David S. Miller" <davem@xxxxxxxxxx>, ak@xxxxxxx, bogdan.costescu@xxxxxxxxxxxxxxxxxxxxx, hadi@xxxxxxxxxxxxxxxx, ralph+d@xxxxxxxxx, xerox@xxxxxxxxxx, sim@xxxxxxxxxxxxx, fw@xxxxxxxxxxxxx, netdev@xxxxxxxxxxx, linux-net@xxxxxxxxxxxxxxx
In-reply-to: <20030610171617.GC1959@xxxxxxx>
References: <Pine.LNX.4.44.0306101801070.26879-100000@xxxxxxxxxxxxxxxxxxxxxxxxxxx> <20030610162029.GA8168@xxxxxxxxxxxxx> <20030610162342.GB1959@xxxxxxx> <20030610.100209.70199702.davem@xxxxxxxxxx> <20030610171617.GC1959@xxxxxxx>
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On Tue, Jun 10, 2003 at 01:16:17PM -0400, Jeff Garzik wrote:
> On Tue, Jun 10, 2003 at 10:02:09AM -0700, David S. Miller wrote:
> >    From: Jeff Garzik <jgarzik@xxxxxxxxx>
> >    Date: Tue, 10 Jun 2003 12:23:42 -0400
> >    
> >    I prefer a compile-time test.
> > 
> > This means end users don't see the benefit, so I definitely
> > prefer Andi's idea.
> Making every IO a conditional branch?  Ug.

An IO takes hundreds or even thousands of cycles. The test and branch
is completely lost in the noise. I bet you won't be able to measure
a difference on any modern CPU.


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