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From: Andi Kleen <ak@suse.de>
To: Arjan van de Ven <arjan@infradead.org>
Subject: Re: [PATCH 1/2] x86-64 TIF flags for debug regs and io bitmap in ctxsw
Date: Tue, 4 Jul 2006 10:09:31 +0200
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On Tuesday 04 July 2006 09:51, Arjan van de Ven wrote:
> > -		}
> > -	}
> > +	if (unlikely((task_thread_info(next_p)->flags & _TIF_WORK_CTXSW))
> > +	    || test_tsk_thread_flag(prev_p, TIF_IO_BITMAP))
> > +		__switch_to_xtra(prev_p, next_p, tss);
> 
> well isn't this replacing an if() (which isn't cheap but also not
> expensive, due to unlikely()) with an atomic operation (which *is*
> expensive) ?

Where do you see an atomic operation?

Also on x86-64 unlikely is an no-op.

-Andi