Subject: Re: 2.6.24-rc6-mm1
From: Peter Zijlstra <peterz@infradead.org>
To: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Ingo Molnar <mingo@elte.hu>, Herbert Xu <herbert@gondor.apana.org.au>,
       Andrew Morton <akpm@linux-foundation.org>, trem <tremyfr@yahoo.fr>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Alan Cox <alan@lxorguk.ukuu.org.uk>
In-Reply-To: <200801022212.29303.nickpiggin@yahoo.com.au>
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Date: Wed, 02 Jan 2008 12:24:07 +0100
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On Wed, 2008-01-02 at 22:12 +1100, Nick Piggin wrote:
> On Wednesday 02 January 2008 22:01, Peter Zijlstra wrote:

> > I've seen 1s+ desktop latencies due to PREEMPT_BKL when I was still
> > using reiserfs.
> 
> Fair enough; so the former ifdefery would be preferable for now then.

To be honest, I must mention that the load that did that was a kernel
build -j5 on a dual socket Athlon MP box. With a current kernel and XFS
that load is making the box slow but its still very servicable.

> > Both reiserfs and tty were fighting for the bkl and massive prio
> > inversion ensued. Turning PREEMPT_BKL off made the system usable again.
> 
> Are either of those subsystems actually using the BKL to protect against
> anything else (than themselves)?

I doubt it.

IIRC Alan is working on getting tty BKL free.

>  It would be sweet to have them use
> private mutexes for the job instead (although even then it probably
> wouldn't be a straight conversion)...

I tried a quick conversion of reiser3 at the time, but it really wants a
recursive lock and I couldn't be bothered to fix a 'legacy' filesystem
so I just gave up and converted the filesystem to XFS.

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