From mboxrd@z Thu Jan  1 00:00:00 1970
From: peterz@infradead.org (Peter Zijlstra)
Date: Fri, 10 Dec 2010 18:49:06 +0100
Subject: [BUG] 2.6.37-rc3 massive interactivity regression on ARM
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To: linux-arm-kernel@lists.infradead.org
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On Fri, 2010-12-10 at 18:18 +0100, Eric Dumazet wrote:
> Le vendredi 10 d?cembre 2010 ? 14:47 +0100, Peter Zijlstra a ?crit :

> Also irq_time_write_begin() and irq_time_write_end() could be faster
> (called for current cpu)
> 
> static inline void irq_time_write_begin(void)
> {
> 	__this_cpu_inc(irq_time_seq.sequence);
> 	smp_wmb();
> }
>  
> static inline void irq_time_write_end(void)
> {
> 	smp_wmb();
> 	__this_cpu_inc(irq_time_seq.sequence);
> }

Yeah, but that kinda defeats the purpose of having it implemented in
seqlock.h. Ideally we'd teach gcc about these long pointers and have
something like: 

  write_seqcount_begin(&this_cpu_read(irq_time_seq));

do the right thing.