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Date: Thu, 11 May 2006 07:05:24 +1000
From: Paul Mackerras <paulus@samba.org>
To: "David S. Miller" <davem@davemloft.net>
Subject: Re: [RFC/PATCH] Make powerpc64 use __thread for per-cpu variables
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David S. Miller writes:

> From: Richard Henderson <rth@twiddle.net>
> Date: Wed, 10 May 2006 08:47:13 -0700
> 
> > How do you plan to address the compiler optimizing
>  ...
> > Across the schedule, we may have changed cpus, making the cached
> > address invalid.
> 
> Per-cpu variables need to be accessed only with preemption
> disabled.  And the preemption enable/disable operations
> provide a compiler memory barrier.

No, Richard has a point, it's not the value that is the concern, it's
the address, which gcc could assume is still valid after a barrier.
Drat.

Paul.