Subject: Re: [patch 1/4] net: percpufy frequently used vars -- add percpu_counter_mod_bh

From: Benjamin LaHaise <[email-masked]>
Date: Wed, 8 Mar 2006 16:17:33 -0500

On Wed, Mar 08, 2006 at 01:07:26PM -0800, Ravikiran G Thirumalai wrote:
> But on non x86, local_bh_disable() is gonna be cheaper than a cli/atomic op no?
> (Even if they were switched over to do local_irq_save() and
> local_irq_restore() from atomic_t's that is).

It's still more expensive than local_t.

> And if we use local_t, we will add the overhead for the non bh 
> percpu_counter_mod for non x86 arches.

Last time I checked, all the major architectures had efficient local_t 
implementations.  Most of the RISC CPUs are able to do a load / store 
conditional implementation that is the same cost (since memory barriers 
tend to be explicite on powerpc).  So why not use it?

		-ben
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