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From: Michael Wang <wangyun@linux.vnet.ibm.com>
To: David Miller <davem@davemloft.net>
Cc: netdev@vger.kernel.org
Subject: Re: [PATCH] Avoid extra calculation in ip_route_input_common
Date: Wed, 21 Dec 2011 14:04:33 +0800	[thread overview]
Message-ID: <4EF176F1.1080802@linux.vnet.ibm.com> (raw)
In-Reply-To: <20111221.005758.556186611596801704.davem@davemloft.net>

On 12/21/2011 01:57 PM, David Miller wrote:

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

Hi, David

Thanks for your detailed explain, now I know the reason we use this style :)

Thanks,
Michael Wang

      reply	other threads:[~2011-12-21  6:04 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-12-21  5:12 [PATCH] Avoid extra calculation in ip_route_input_common Michael Wang
2011-12-21  5:19 ` Michael Wang
2011-12-21  5:23 ` Joe Perches
2011-12-21  5:39   ` Michael Wang
2011-12-21  5:50     ` Joe Perches
2011-12-21  6:00       ` Michael Wang
2011-12-21  5:57 ` David Miller
2011-12-21  6:04   ` Michael Wang [this message]

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