Re: stochastic fair queueing in the elevator [Re: [BENCHMARK] 2.4.20-ck3 / aa / rmap with contest]

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On Mon, 10 Feb 2003 06:10:08 +0100, Jakob Oestergaard said:

> In stock 2.4.20 the interaction is horrible - whatever was done there i=
s
> not optimal.    A 'tar xf' on the client will neither load the network
> nor the server - it seems to be network latency bound (readahead not
> doing it's job - changing min-readahead and max-readahead on the client=

> doesn't seem to make a difference). However, my desktop (running on the=

This sounds like the traditional NFS suckage that has been there for deca=
des.
The problem is that 'tar xf' ends up doing a *LOT* of NFS calls - a huge
stream of stat()/open()/chmod()/utime() calls.  On a local disk, most of
this gets accelerated by the in-core inode cache, but on an NFS mount, yo=
u're
looking at lots and lots of synchronous calls.

In 'man 5 exports':

       async  This option allows the NFS server to violate  the  NFS  pro=
tocol
              and  reply  to  requests before any changes made by that re=
quest
              have been committed to stable storage (e.g. disc drive).

              Using this option usually improves performance, but at the =
 cost
              that  an unclean server restart (i.e. a crash) can cause da=
ta to
              be lost or corrupted.

              In releases of nfs-utils upto and including 1.0.0,  this  o=
ption
              was  the  default.   In  this  and  future releases, sync i=
s the
              default, and async must be explicit  requested  if  needed.=
   To
              help  make system adminstrators aware of this change, 'expo=
rtfs'
              will issue a warning if neither sync nor async is specified=
=2E

Does this address your NFS issue?
-- =

				Valdis Kletnieks
				Computer Systems Senior Engineer
				Virginia Tech

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