linux-kernel - Re: high latency NFS

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Message-ID: <20080804003206.GB6119@disturbed>
Date:	Mon, 4 Aug 2008 10:32:06 +1000
From:	Dave Chinner <david@...morbit.com>
To:	"J. Bruce Fields" <bfields@...ldses.org>
Cc:	Neil Brown <neilb@...e.de>, Michael Shuey <shuey@...due.edu>,
	Shehjar Tikoo <shehjart@....unsw.edu.au>,
	linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org,
	rees@...i.umich.edu, aglo@...i.umich.edu
Subject: Re: high latency NFS

On Fri, Aug 01, 2008 at 03:15:59PM -0400, J. Bruce Fields wrote:
> On Fri, Aug 01, 2008 at 05:23:20PM +1000, Dave Chinner wrote:
> > On Thu, Jul 31, 2008 at 05:03:05PM +1000, Neil Brown wrote:
> > > You might want to track the max length of the request queue too and
> > > start more threads if the queue is long, to allow a quick ramp-up.
> > 
> > Right, but even request queue depth is not a good indicator. You
> > need to leep track of how many NFSDs are actually doing useful
> > work. That is, if you've got an NFSD on the CPU that is hitting
> > the cache and not blocking, you don't need more NFSDs to handle
> > that load because they can't do any more work than the NFSD
> > that is currently running is. 
> > 
> > i.e. take the solution that Greg banks used for the CPU scheduler
> > overload issue (limiting the number of nfsds woken but not yet on
> > the CPU),
> 
> I don't remember that, or wasn't watching when it happened.... Do you
> have a pointer?

Ah, I thought that had been sent to mainline because it was
mentioned in his LCA talk at the start of the year. Slides
65-67 here:

http://mirror.linux.org.au/pub/linux.conf.au/2007/video/talks/41.pdf

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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