netdev - Re: [PERCPU] Remove & in front of this_cpu

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Date:	Thu, 4 Apr 2013 13:52:00 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
cc:	Tejun Heo <htejun@...il.com>, RongQing Li <roy.qing.li@...il.com>,
	Shan Wei <davidshan@...cent.com>, netdev@...r.kernel.org
Subject: Re: [PERCPU] Remove & in front of this_cpu_ptr

On Wed, 3 Apr 2013, Eric Dumazet wrote:

> I agree with you, I prefer &this_cpu_ptr(percpu_pointer)->field
>
> The offset is added after getting the address of the (percpu) base
> object.

There are two offsets being added! percpu_pointer is not a
pointer but an offset. this_cpu_ptr creates a pointer from the
percpu base of the current processor by adding the offset of the percpu
variable. The offset calculation better be in the parenthesis.

The method that I proposed is also conforming with the use of other
this_cpu_ops. F.e. In order to do a read one would need to do

x = this_cpu_read(percpu_pointer->field)

x = this_cpu_read(percpu_pointer)->field

does not work (and does not pass sparse).

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