linux-kernel - Re: [PATCH] atomic: add atomic_inc_not_zero

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Message-ID: <1288984371.2665.13.camel@edumazet-laptop>
Date:	Fri, 05 Nov 2010 20:12:51 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, Andi Kleen <andi@...stfloor.org>,
	Nick Piggin <npiggin@...nel.dk>
Subject: Re: [PATCH] atomic: add atomic_inc_not_zero_hint()

Le vendredi 05 novembre 2010 à 11:40 -0700, Paul E. McKenney a écrit :

> OK, so I cannot resist the challenge...  ;-)
> 

I knew that ;)

> Suppose that the atomic_inc_not_zero_hint() is in common code that might
> be invoked from a cleanup path.  On the cleanup path, perhaps within an
> RCU callback, if the reference is zero, we have the only reference and
> thus don't need to increment the reference count.  On the other hand,
> if the reference is non-zero, we want to obtain a reference in order
> to safely attempt to encourage the other reference holder to let go
> more quickly.
> 
> Perhaps a bit of a stretch, but why not just replace the above
> "return 0" with "atomic_inc_not_zero(v)"?  It will usually be
> compiled out, right?

Yes indeed, thanks !



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