Date: Sun, 28 Jan 2007 10:01:32 -0800
To: "Martin J. Bligh" <mbligh@mbligh.org>
Cc: Christoph Hellwig <hch@infradead.org>, Ingo Molnar <mingo@elte.hu>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>, Andrew Morton <akpm@osdl.org>,
       linux-kernel@vger.kernel.org, Dipankar Sarma <dipankar@hill9.org>,
       "Bill Huey (hui)" <billh@gnuppy.monkey.org>
Subject: Re: lockmeter
Message-ID: <20070128180132.GA1647@gnuppy.monkey.org>
References: <20070128115118.837777000@programming.kicks-ass.net> <20070128144325.GB16552@infradead.org> <20070128152404.GB9196@elte.hu> <45BCD4C9.2030302@mbligh.org> <20070128170407.GA1526@infradead.org> <45BCDF88.2020504@mbligh.org>
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From: Bill Huey (hui) <billh@gnuppy.monkey.org>
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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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