linux-kernel - Re: [PATCH] AFS: Fix file locking

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Message-ID: <a781481a0707230150u21ba14bfme7bbff92d4705d20@mail.gmail.com>
Date:	Mon, 23 Jul 2007 14:20:56 +0530
From:	"Satyam Sharma" <satyam.sharma@...il.com>
To:	"Nick Piggin" <nickpiggin@...oo.com.au>
Cc:	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] AFS: Fix file locking

Hi,

On 7/23/07, Nick Piggin <nickpiggin@...oo.com.au> wrote:
> Linus Torvalds wrote:
> >
> > On Fri, 20 Jul 2007, Nick Piggin wrote:
> >
> >>So you did. Then to answer that, yes it could be faster because there are
> >>stupid volatiles sprinkled all over the bitops code so you could easily
> >>end up having to do more loads. Does it make a real difference? Unlikely,
> >>but David loves counting cycles :)
> >
> >
> > I thought we long long since removed the volatiles. They are buggy and
> > horrible, and we really want to let the compiler combine multiple
> > test-bits, and if they matter that implies locking is buggy or something
> > worse..
> >
> > Ie we'd *want*
> >
> >       if (test_bit(x, y) || test_bit(z,y))
> >
> > to be rewritten by the compiler as testing bits x/z at the same time.
>
> Yep. We'd also want __set_bit(x, y); __set_bit(z, y); and such to be
> combined.
> >
> > But now I'm too scared to look.
>
> Not a chance :) Even the asm-generic "reference" implementation ratifies
> the volatile crapiness. Would you take a patch?

Coincidentally, I'm working on a cleanup of the bitops code just now --
I stumbled upon a lot of varied bogosity in there :-) Intend to send it
out in a couple of hours, probably.

Satyam
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