linux-kernel - Re: linux-next: percpu tree build warning

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Message-Id: <200911282021.50315.rusty@rustcorp.com.au>
Date:	Sat, 28 Nov 2009 20:21:50 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Tejun Heo <tj@...nel.org>, Stephen Rothwell <sfr@...b.auug.org.au>,
	"Fr??d??ric Weisbecker" <fweisbec@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Christoph Lameter <cl@...ux-foundation.org>,
	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: linux-next: percpu tree build warning

On Fri, 27 Nov 2009 04:11:28 pm Ingo Molnar wrote:
> 
> * Rusty Russell <rusty@...tcorp.com.au> wrote:
> 
> > On Thu, 26 Nov 2009 12:10:58 am Ingo Molnar wrote:
> > > While a percpu variable is defined and used in completely different 
> > > ways:
> > > 
> > >   DEFINE_PER_CPU(unsigned long, dr7);
> > > 
> > > and is used via:
> > > 
> > >   __get_cpu_var(dr7);  [[Fixed -- RR]]
> > 
> > The entire point of Tejun's per-cpu work is that &dr7 is now valid. A 
> > per-cpu pointer as if it were allocated by the dynamic per-cpu 
> > allocator.
> >
> > Your arguments are fine, but out-of-date.
> 
> But allowing &dr7 is outright dangerous - and not particularly clean 
> either.

That's foolish.  We can now have generic per-cpu function for counters
and the like.

> Nothing tells us that it's a percpu variable

__percpu.  Again, I'm explaining what you should already know before sending
email about this stuff.

> and it blends into the 
> regular namespace while most of the operators on it are special 
> (__get_cpu_var(), per_cpu(), __this_cpu(), etc.).

OK, you convince Linus to change __user vars to use a prefix.  Then I'll
agree that per_cpu_## is more kernely.

Stupidest debate ever.
Rusty.
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