linux-kernel - Re: [PATCH v4 3/9] net: xfrm: use __this_cpu

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Message-ID: <50A213DF.1040103@gmail.com>
Date:	Tue, 13 Nov 2012 17:33:19 +0800
From:	Shan Wei <shanwei88@...il.com>
To:	Steffen Klassert <steffen.klassert@...unet.com>,
	Christoph Lameter <cl@...ux.com>
CC:	David Miller <davem@...emloft.net>,
	NetDev <netdev@...r.kernel.org>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Kernel-Maillist <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 3/9] net: xfrm: use __this_cpu_read per-cpu helper

Steffen Klassert said, at 2012/11/13 15:21:
> 
> This should just fetch the tfm pointer, so why exactly __this_cpu_read
> is better than __this_cpu_ptr? Please keep in mind that performance is
> not the most important thing here. It's much more important that it
> works in any case.
 
[0/9] describes why we should submit this series patches.
you are not included in original mail.

this_cpu_ptr relocates and address. this_cpu_read() relocates the address
and performs the fetch. If you want to operate on rda(defined as per_cpu) 
then you can only use this_cpu_ptr. this_cpu_read() saves you more instructions
since it can do the relocation and the fetch in one instruction.

More info, please refer to http://www.spinics.net/lists/kernel/msg1435153.html

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