linux-kernel - Re: [patch 04/41] cpu ops: Core piece for generic atomic per cpu operations

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Message-Id: <1213263470.25502.6.camel@kitka.ibm.com>
Date:	Thu, 12 Jun 2008 11:37:49 +0200
From:	Martin Peschke <mp3@...ibm.com>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Christoph Lameter <clameter@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	David Miller <davem@...emloft.net>,
	Eric Dumazet <dada1@...mosbay.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Mike Travis <travis@....com>
Subject: Re: [patch 04/41] cpu ops: Core piece for generic atomic per cpu
	operations

On Thu, 2008-06-12 at 13:40 +1000, Nick Piggin wrote:
> On Thursday 12 June 2008 12:44, Rusty Russell wrote:
> > On Thursday 12 June 2008 10:58:01 Nick Piggin wrote:
> > > On Thursday 12 June 2008 09:39, Christoph Lameter wrote:
> > > > On Wed, 11 Jun 2008, Rusty Russell wrote:
> > > > > > 4. The modeling of local_t on atomic_t limits it to 32bit!
> > > > >
> > > > > Again wrong.  And adding an exclamation mark doesn't make it true.
> > > >
> > > > Ewww ... Its atomic_long_t ahh. Ok then there no 32 bit support. What
> > > > about pointers?
> > >
> > > sizeof(long) == sizeof(void *) in Linux, right?
> > >
> > > If you were to support just a single data type, long would probably
> > > be the most useful. Still, it might be more consistent to support
> > > int and long, same as atomic.
> >
> > Sure, but in practice these tend to be simple counters: that could well
> > change when dynamic percpu allocs become first class citizens, but let's
> > not put the cart before the horse...
> 
> Right, I was just responding to Christoph's puzzling question.
> 
> 
> > Per-cpu seems to be particularly prone to over-engineering: see commit
> > 7ff6f08295d90ab20d25200ef485ebb45b1b8d71 from almost two years ago. 
> > Grepping here reveals that this infrastructure is still not used.
> 
> Hmm. Something like that needs the question asked "who uses this?"
> before it is merged I guess. If it were a trivial patch maybe not,
> but something like this that sits untested for so long is almost
> broken by definition ;)

Some code of mine which didn't make it beyond -mm used this small
per-cpu extension. So the commit you refer to was tested.

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