kern/131360: [nfs] poor scaling behavior of the NFS server under load

[Martin Birgmeier]

The following reply was made to PR kern/131360; it has been noted by GNATS.

From: Martin Birgmeier <martin at email.aon.at>
To: bug-followup at FreeBSD.org
Cc:  
Subject: Re: kern/131360: [nfs] poor scaling behavior of the NFS server under load
Date: Sat, 7 Feb 2009 16:31:21 +0100 (CET)

 I am now very sure that this is an interaction with pppoa, and it is
 also worse than I originally thought: it will even lead to failed NFS
 transactions for the client.
 
 Here is what I have:
 
 Machine A ('server', a mini home server) does the following:
   - connecting to the Internet using usermode ppp over pppoa over an
     Alcatel ADSL modem
   - NFS serving FreeBSD sources
 
 Machine B does the following:
   - Mounting the FreeBSD sources from A (using amd), under directory
     /vol/SRC/FreeBSD/HEAD/src
   - Compiling the FreeBSD sources: make -j4 buildworld, such that the
     corresponding obj is local (via amd again)
 
 Especially in the first phase of the buildworld (clean, depend, obj),
 there is a lot of simultaneous NFS traffic from B to A. As soon as
 a download is started at A (going via pppoa, of course), the load on
 A rises to very high values (> 20 not uncommon).
 
 This may lead to B aborting the compile, it just did that with
 "directory not found".
 
 Both machines are running 7.1.0.
 
 No such problem happended when both were running 6.3.0.