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

Date: Mon Feb 10 2003 - 01:06:27 EST

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 is
> 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 decades.
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, you're
looking at lots and lots of synchronous calls.

In 'man 5 exports':

       async This option allows the NFS server to violate the NFS protocol
              and reply to requests before any changes made by that request
              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 data to
              be lost or corrupted.

              In releases of nfs-utils upto and including 1.0.0, this option
              was the default. In this and future releases, sync is the
              default, and async must be explicit requested if needed. To
              help make system adminstrators aware of this change, 'exportfs'
              will issue a warning if neither sync nor async is specified.

Does this address your NFS issue?

				Valdis Kletnieks
				Computer Systems Senior Engineer
				Virginia Tech

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