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

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Date:	Wed, 18 Jul 2007 15:56:53 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	David Howells <dhowells@...hat.com>, torvalds@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] AFS: Fix file locking

Andrew Morton wrote:
> On Tue, 17 Jul 2007 13:47:32 +0100
> David Howells <dhowells@...hat.com> wrote:
> 
> 
>>+	if (type == AFS_LOCK_READ &&
>>+	    vnode->flags & (1 << AFS_VNODE_READLOCKED)) {
> 
> 
> Here we use
> 
> 	vnode->flags & (1 << foo)
> 
> 
>>+		set_bit(AFS_VNODE_LOCKING, &vnode->flags);
> 
> 
> and elsewhere we use set_bit(foo, &vnode->flags) and clear_bit()
> 
> This is a bit strange.  Does the open-coded bit-test have any performance
> benefit on any architecture?  Not on x86 at least, afaik.

It uses locked operations on x86, but you can use __set_bit instead
(which should always be at least as efficient as the C version).

-- 
SUSE Labs, Novell Inc.
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