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

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Message-Id: <200806121244.12173.rusty@rustcorp.com.au>
Date:	Thu, 12 Jun 2008 12:44:11 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	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>, Martin Peschke <mp3@...ibm.com>
Subject: Re: [patch 04/41] cpu ops: Core piece for generic atomic per cpu operations

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...

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.

Cheers,
Rusty.
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