[nfsv4] Performance drop in iozone for reading large files

[Trond Myklebust]

On Fri, 2006-08-25 at 15:57 -0700, Bryce Harrington wrote:
> On Fri, Aug 25, 2006 at 05:23:37PM -0400, Trond Myklebust wrote:
> > On Fri, 2006-08-25 at 14:01 -0700, Bryce Harrington wrote:
> > > There is a performance issue in READ operations we've noticed in iozone
> > > runs for a while now.  If you look at this plot, of NFSv4 with 1G mem:
> > > 
> > >    http://crucible.osdl.org/runs/1604/test_output/iozone.sys.log.png
> > > 
> > > You can see that we're getting fairly steady performance up until the
> > > 1048576kb case, where read performance drops to about a third.
> > 
> > Is the readahead algorithm working correctly? Could you please try
> > applying the following patch, and then check your syslog for warnings?
> 
> Here it is:
> 
> http://crucible.osdl.org/runs/1617/nfs03.console.log
> 
> Looks like it switches between 12K, 240K, and 60K.  Does that sound
> right?
> 
> Thanks,
> Bryce

OK. Could you try the attached patch? It ought to fix that particular
issue. I'm curious to see if it will also fix the performance problem.

Cheers,
  Trond
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