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Subject: Re: [PATCH] x86: Replace uses of current_cpu_data with this_cpu ops
From: Eric Dumazet <eric.dumazet@gmail.com>
To: Christoph Lameter <cl@linux.com>
Cc: Tejun Heo <tj@kernel.org>, akpm@linux-foundation.org,
        Yinghai Lu <yinghai@kernel.org>, Ingo Molnar <mingo@elte.hu>,
        Pekka Enberg <penberg@cs.helsinki.fi>, linux-kernel@vger.kernel.org,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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Date: Wed, 08 Dec 2010 18:17:26 +0100
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Le mercredi 08 décembre 2010 à 09:33 -0600, Christoph Lameter a écrit :
> On Wed, 8 Dec 2010, Eric Dumazet wrote:
> 
> > > In the long run, it might be a good idea to remove cpu_data() macro
> > > too and use per_cpu macro directly.
> > >
> >
> > or introduce this_cpu_has() to remove the adress computation
> >
> > -	if (cpu_has(__this_cpu_ptr(&cpu_info), X86_FEATURE_ARAT)) {
> >
> > +	if (this_cpu_has(X86_FEATURE_ARAT)) {
> >
> 
> The fundamental problem is that bitops require memory addresses which does
> not work with per cpu ops.
> 

Sure, set() or clear() needs the address, but the read doesnt ?

This can be implemented as

  (__this_cpu_read(cpu_info.word[X]) & MASK)

Anyway, even if mapped to cpu_has(__this_cpu_ptr(&cpu_info), XXX), 
it would be cleaner to use this_cpu_has() helper.