Re: [PATCH 1/2] x86-64 TIF flags for debug regs and io bitmap inctxsw

[Arjan van de Ven]

On Tue, 2006-07-04 at 10:09 +0200, Andi Kleen wrote:
> 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?

test_tsk_thread_flag() ends up doing an atomic op afaics


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