linux-kernel - Re: [PATCH 22/25] Generic dynamic per cpu refcounting

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Message-ID: <20121129185953.GW16230@one.firstfloor.org>
Date:	Thu, 29 Nov 2012 19:59:53 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Kent Overstreet <koverstreet@...gle.com>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	linux-aio@...ck.org, linux-fsdevel@...r.kernel.org, zab@...hat.com,
	bcrl@...ck.org, jmoyer@...hat.com, axboe@...nel.dk,
	viro@...iv.linux.org.uk
Subject: Re: [PATCH 22/25] Generic dynamic per cpu refcounting

On Thu, Nov 29, 2012 at 10:57:20AM -0800, Kent Overstreet wrote:
> On Thu, Nov 29, 2012 at 10:45:04AM -0800, Andi Kleen wrote:
> > Kent Overstreet <koverstreet@...gle.com> writes:
> > 
> > > This implements a refcount with similar semantics to
> > > atomic_get()/atomic_dec_and_test(), that starts out as just an atomic_t
> > > but dynamically switches to per cpu refcounting when the rate of
> > > gets/puts becomes too high.
> > 
> > This will only work if you put on the same CPU as you get, right?
> 
> Nope, no such restriction.

I don't see how you ensure you're doing the __this_cpu_dec on the same
CPU as you did the get

-Andi
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