linux-kernel - Re: [PATCH v2 6/9] rcu: use __this_cpu_read helper instead of per_cpu_ptr(p, raw_smp_processor

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Message-ID: <0000013ad148e92a-ea123f83-e6f6-4131-8e15-8cf05cfd1e0a-000000@email.amazonses.com>
Date:	Mon, 5 Nov 2012 15:55:47 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	单卫 <shanwei88@...il.com>
cc:	paulmck@...ux.vnet.ibm.com, dipankar@...ibm.com,
	Kernel-Maillist <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 6/9] rcu: use __this_cpu_read helper instead of
 per_cpu_ptr(p, raw_smp_processor_id())

On Mon, 5 Nov 2012, 锟斤拷锟斤拷 wrote:

> I guarantee that x86-64 don't use gs register here. run test again锟斤拷
> Maybe there is some optimizations for __this_cpu_read call on x86-64锟斤拷 not
> sure.

There is no optimization that I know of unless the compiler eliminated the
__this_cpu_read completely. gs: is necessary to perform the implied
relocation in this_cpu_read().