From: Nick Piggin <nickpiggin@yahoo.com.au>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] AFS: Fix file locking
Date: Mon, 23 Jul 2007 17:07:09 +1000 [thread overview]
Message-ID: <46A4539D.9060100@yahoo.com.au> (raw)
In-Reply-To: <alpine.LFD.0.999.0707201835070.27249@woody.linux-foundation.org>
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?
--
SUSE Labs, Novell Inc.
next prev parent reply other threads:[~2007-07-23 7:07 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-07-17 12:47 [PATCH] AFS: Fix file locking David Howells
2007-07-18 0:50 ` Andrew Morton
2007-07-18 5:56 ` Nick Piggin
2007-07-20 3:41 ` Andrew Morton
2007-07-20 4:59 ` Nick Piggin
2007-07-21 1:37 ` Linus Torvalds
2007-07-23 7:07 ` Nick Piggin [this message]
2007-07-23 8:50 ` Satyam Sharma
2007-07-23 9:13 ` Satyam Sharma
2007-07-23 9:13 ` David Howells
2007-07-18 9:23 ` David Howells
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