linux-kernel - Re: [GIT PATCH] TTY patches for 2.6.33-git

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Message-ID: <20091213213015.653307b5@infradead.org>
Date:	Sun, 13 Dec 2009 21:30:15 -0800
From:	Arjan van de Ven <arjan@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg KH <gregkh@...e.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org
Subject: Re: [GIT PATCH] TTY patches for 2.6.33-git

On Sun, 13 Dec 2009 20:16:08 +0100
Frederic Weisbecker <fweisbec@...il.com> wrote:

> On Sun, Dec 13, 2009 at 09:55:34AM -0800, Arjan van de Ven wrote:
> > On Sun, 13 Dec 2009 07:58:44 +0100
> > Ingo Molnar <mingo@...e.hu> wrote:
> > 
> > > 
> > > * Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> > > 
> > > > We've had quite a bit of BKL work this merge-window. Maybe we'll
> > > > even get rid of it one of these days. There are "only" about 600
> > > > instances of "lock_kernel()" in the tree right now ;)
> > > 
> > > I tend to use unlock_kernel() as the metric. (as it's more
> > > precisely greppable and it is also more indicative of the
> > > underlying complexity of locking, as it gets used more in more
> > > complex scenarios)
> > 
> > another metric is... how many times do we take the BKL for some
> > workload. (For example booting or compiling a kernel).
> > A counter like "BKLs-per-second" would be nice to expose
> > (and then we can track that number going up as a regression etc)
> 
> 
> 
> We have the bkl tracepoints for that, attaching an example below,
> blkdev_get/bkldev_put is among the highest consumer for me.

we have a trace, but not a number that anyone can just pull out without
having to go through great lengths to set stuff up... (esp to capture a
boot)...
Adding a counter always to the lock_kernel function should be fine
instead...


-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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