linux-kernel - Re: [PATCH 4/7] ufs: remove the BKL

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Message-ID: <20110302154842.GA32314@elliptictech.com>
Date:	Wed, 2 Mar 2011 10:48:42 -0500
From:	Nick Bowler <nbowler@...iptictech.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-kernel@...r.kernel.org,
	Evgeniy Dushistov <dushistov@...l.ru>,
	Nick Piggin <npiggin@...il.com>
Subject: Re: [PATCH 4/7] ufs: remove the BKL

On 2011-03-02 16:08 +0100, Arnd Bergmann wrote:
> On Wednesday 02 March 2011, Nick Bowler wrote:
> > On 2011-03-02 00:13 +0100, Arnd Bergmann wrote:
> > > The code is still only compile-tested,
> > 
> > This isn't true anymore; I've been running with this patch (well, the
> > previous versions thereof) for some time now.  On the other hand, I
> > don't use all of this driver's features.
> 
> I'll updated the comment. Can I add your Tested-by tag?

Sure.

> > > but it should at least be harmless on non-SMP systems, since the new
> > > mutex is not taken on those.
> > 
> > I think this part of the patch is strange.  It seems like a gratuitous
> > difference between SMP/preempt and other systems to #if out the code
> > that takes the mutex.  This might make problems with the conversion fly
> > under the radar longer because people with older systems won't encounter
> > them.
> 
> I agree it is strange, but the mutex has some serious performance impact
> that I wanted to minimize on the systems where we know it is not needed.
> The BKL was only active on those systems, so we know that non-SMP
> non-preempt kernels don't need the mutex.

Fair enough.  If it hurts too much to run this code when it's not
needed, then I guess it makes sense to leave it out.

-- 
Nick Bowler, Elliptic Technologies (http://www.elliptictech.com/)
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