linux-kernel - Re: [PATCH] x86: remove byte locks

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Date:	Thu, 15 Jan 2009 11:55:01 +0100 (CET)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
cc:	Ingo Molnar <mingo@...e.hu>,
	Jeremy Fitzhardinge <jeremy@...source.com>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86: remove byte locks

On Tue, 13 Jan 2009, Jeremy Fitzhardinge wrote:

> > Why can't this just be somewhere in documentation? (possibly even with 
> > the byte locks code as a reference).
> Because Ingo's compil-o-matic will never fail on a documentation error.

Hmm, I have always considered the "we don't accept any code that would 
have zero in-kernel users" rule as a quite reasonable one, at least in 
order to prevent from bloat and code getting confusing.
But apparently it's not the intention here.

> > It is IMHO just totally confusing to have a spinlock implementation that is
> > not used at all in the tree. It took me quite some time to go through this
> > until I finally figured out that this code is actually never used.
> > Currently, on first sight it might seem that byte locks are used whenever
> > CONFIG_PARAVIRT is set, which is not true.
> Well, a comment next to the code explaining the rationale probably 
> wouldn't go astray.

I still strongly feel that if the only purpose of the code in kernel is 
"to provide example", then it belongs to documentation.

> > And apparently even Linus got confused by this, which also tells us
> > something by itself, see [1].
> > [1] http://marc.info/?l=linux-kernel&m=123144211719754&w=2
> It tells us that Linus couldn't give a rat's arse about virtualization, 
> which is just something we have to cope with ;)

I am afraid this has nothing to do with virtualization. It's simply 
confusing when looking at the code.

Thanks,

-- 
Jiri Kosina
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