netdev - Re: [PATCH] Avoid extra calculation in ip_route_input

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Message-Id: <20111221.005758.556186611596801704.davem@davemloft.net>
Date:	Wed, 21 Dec 2011 00:57:58 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	wangyun@...ux.vnet.ibm.com
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] Avoid extra calculation in ip_route_input_common

From: Michael Wang <wangyun@...ux.vnet.ibm.com>
Date: Wed, 21 Dec 2011 13:12:03 +0800

> From: Michael Wang <wangyun@...ux.vnet.ibm.com>
> 
> If previous condition doesn't meet, the later check will be cancelled.
> So we don't need to do all the calculation.
> 
> Signed-off-by: Michael Wang <wangyun@...ux.vnet.ibm.com>

This is intentional to reduce the number of branch prediction
misses, please don't change this.

Once we read one of these values, the rest are incredibly cheap,
the real cost is if we have tons of real branches here, each
of which can be mispredicted.
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