Terrible NFS performance under 9.2-RELEASE?

[Rick Macklem]

Garrett Wollman wrote:
> <<On Sat, 25 Jan 2014 21:36:26 -0500 (EST), Rick Macklem
> <rmacklem at uoguelph.ca> said:
> 
> > Have you tried increasing readahead by any chance? I think the
> > default
> > is 1, which means the client will make 2 read requests and then
> > wait for
> > those replies before doing any more reads. Since you have fast
> > links,
> > maybe the 2 * 64K reads isn't enough to keep the pipe filled? (This
> > depends on latency, which you didn't mention.)
> 
> -o readahead=4 nearly doubles the speed, to a bit over 5 Gbit/s.
> 
And "-o readahead=8" is slower or faster? (I think you can go up to at
least 16, but I can't remember the upper bound. It's in one of the
.h files.;-)

> Oddly, when I unmount the filesystem, the test client sometimes
> freezes for 15-30 seconds.  Since I'm not on the console I can't tell
> what it's doing when this happens.
> 
Hmm, no idea. Maybe it takes a while to throw away all the buffer cache
blocks?

I run such small systems by to-days standards, I wouldn't see a delay
that "might" occur for a large buffer cache.

At least a little progress, rick

> -GAWollman
> 
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