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Date: Fri, 13 Jul 2007 14:45:02 +0200
From: Christoph Hellwig <hch@lst.de>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: [PATCH 1/2] Enable SPU switch notification to detect currently
	active SPU tasks.
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Cc: Philippe Elie <phil.el@wanadoo.fr>, linuxppc <linuxppc-dev@ozlabs.org>,
	Bob Nelson <rrnelson@linux.vnet.ibm.com>,
	oprofile <oprofile-list@lists.sourceforge.net>,
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On Fri, Jul 13, 2007 at 10:34:50PM +1000, Benjamin Herrenschmidt wrote:
> 
> > > +		if (unlikely(test_bit(SPU_SCHED_NOTIFY_ACTIVE,
> > > +				      &ctx->sched_flags))) {
> > > +			clear_bit(SPU_SCHED_NOTIFY_ACTIVE, &ctx->sched_flags);
> > 
> > this should use test_and_clear_bit
> 
> This also looks like an abuse of atomics to effectively implement a lock
> or did I miss something ?

not really.  We set a flag on the context to make sure some action is
performed when it comes through spu_run the next time.  It's not exactly
elegant, but cleaning this up will have to wait for the grand spu_run
rewrite.