Re: [PATCH] AFS: Fix file locking

Andrew Morton
2007-07-20T03:41:33Z

On Wed, 18 Jul 2007 15:56:53 +1000 Nick Piggin <nickpiggin@yahoo.com.au> wrote:

> Andrew Morton wrote:
> > On Tue, 17 Jul 2007 13:47:32 +0100
> > David Howells <dhowells@redhat.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).

I said "bit-test". ie: test_bit(). That doesn't use a locked operation.