linux-kernel - Re: lockmeter

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Message-ID: <20070128180132.GA1647@gnuppy.monkey.org>
Date:	Sun, 28 Jan 2007 10:01:32 -0800
From:	Bill Huey (hui) <billh@...ppy.monkey.org>
To:	"Martin J. Bligh" <mbligh@...igh.org>
Cc:	Christoph Hellwig <hch@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org,
	Dipankar Sarma <dipankar@...l9.org>,
	"Bill Huey (hui)" <billh@...ppy.monkey.org>
Subject: Re: lockmeter

On Sun, Jan 28, 2007 at 09:38:16AM -0800, Martin J. Bligh wrote:
> Christoph Hellwig wrote:
> >On Sun, Jan 28, 2007 at 08:52:25AM -0800, Martin J. Bligh wrote:
> >>Mmm. not wholly convinced that's true. Whilst i don't have lockmeter
> >>stats to hand, the heavy time in __d_lookup seems to indicate we may
> >>still have a problem to me. I guess we could move the spinlocks out
> >>of line again to test this fairly easily (or get lockmeter upstream).
> >
> >We definitly should get lockmeter in.  Does anyone volunteer for doing
> >the cleanup and merged?
> 
> On second thoughts .. I don't think it'd actually work for this since
> the locks aren't global. Not that it shouldn't be done anyway, but ...
> 
> ISTR we still thought dcache scalability was a significant problem last
> time anyone looked at it seriously - just never got fixed. Dipankar?

My lock stat stuff shows dcache to a be a problem under -rt as well. It
is keyed off the same mechanism as lockdep. It's pretty heavily hit
under even normal loads relative to other kinds of lock overhead even
for casual file operations on a 2x system. I can't imagine how lousy
it's going to be under real load on a 8x or higher machine.

However, this pathc is -rt only and spinlock times are meaningless under
it because of preemptiblity.

bill

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