Re: [xfs-masters] RFC: Fix f_flags races without the BKL

[Andi Kleen <andi@firstfloor.org>]

On Tue, Dec 30, 2008 at 02:04:39PM +0100, Christoph Hellwig wrote:
> On Tue, Dec 30, 2008 at 05:59:56AM -0700, Jonathan Corbet wrote:
> > On Mon, 29 Dec 2008 16:27:32 +0100
> > Andi Kleen <andi@firstfloor.org> wrote:
> > 
> > > I would prefer O_LOCK_FLAGS bit too. The global lock is not very nice
> > > and I don't doubt someone will come up with a workload which
> > > pounds on it.
> > 
> > Seems hard to imagine that it would be worse than the longstanding BKL
> > situation.  That said, the global lock is clearly an unsubtle approach,
> > and people don't like it.  I'd hoped to slip something quick through
> > the merge window, but that seems unlikely, especially, since I'm
> > allegedly on vacation.  I'll forget this patch for now and revisit it
> > next week.
> 
> The global lock is an improvement over the current situation, so given
> that we don't have any better counter-proposals we should put it in for
> 2.6.29.

That's not clear. Mutexes can be much slower than a spinlock
like BKL in some situations, mostly because they schedule more and
have generally more overhead.

As long as you don't have another BKL user contending the BKL
is likely faster than the mutex.

-Andi

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