linux-kernel - Re: [PATCH 3/3] x86: OLPC: speed up device tree creation during boot (v2)

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Message-ID: <1290078135.22575.4.camel@concordia>
Date:	Thu, 18 Nov 2010 22:02:15 +1100
From:	Michael Ellerman <michael@...erman.id.au>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	devicetree-discuss@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	Milton Miller <miltonm@....com>,
	Ingo Molnar <mingo@...hat.com>,
	Andres Salomon <dilinger@...ued.net>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 3/3] x86: OLPC: speed up device tree creation during
 boot (v2)

On Thu, 2010-11-18 at 09:34 +0100, Ingo Molnar wrote:
> * H. Peter Anvin <hpa@...or.com> wrote:
> 
> > On 11/14/2010 11:02 PM, Ingo Molnar wrote:
> > > 
> > > * H. Peter Anvin <hpa@...or.com> wrote:
> > > 
> > >> What?  What is wrong with static variables in functions?  It really doesn't seem 
> > >> to be a good idea to make them file-scope if they don't need to be.
> > > 
> > > They are very easy to overlook and mix up with regular stack variables and i've seen 
> > > (and introduced myself) a number of bugs due to them.
> > > 
> > > They also often are used in buggy ways (with SMP not taken into consideration), so 
> > > overlooking them during review compounds their negative effects. Putting them in 
> > > front of the function isnt a big deal in exchange.
> > > 
> > > There are people who never overlook them (like yourself), but my brain is wired up 
> > > differently.
> > > 
> > 
> > However, I have to vehemently object to putting them in a wider scope
> > than is otherwise necessary.  I agree that static variables should be
> > used sparsely if at all (there really are vary few uses of them that are
> > valid), but putting them in a larger scope screams "I'm used in more
> > than one function", and that is *not* a good thing.
> 
> That's why we sometimes use the (imperfect) compromise to put them in front of that 
> function, not at the top of the file.
> 
> Look at the general balance of hardship: very little harm is done (it's not a big 
> deal if a variable is only used in a single function) but having it with local 
> variables can be _really_ harmful - for example i overlooked them when i reviewed 
> this patch. I dont like important details obscured - i like them to be apparent. 
> Again, this is something that some people can parse immediately on the visual level 
> - me and many others cannot.

What about:

int foo(void)
{
	static int bar;

	struct thing_struct *thing;
	int other_var;
	char *p;

	...
}

I think the visual wrongness of that formatting would be enough for me
to stop and look twice. Though I guess it doesn't work if you have few,
or no other variables other than the statics to declare.

cheers


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