Re: 2.6.30-rc deadline scheduler performance regression for iozoneover NFS

[Jim Rees]

Andrew Morton wrote:

  Jeff's computer got slower.  Can we fix that?

TCP autotuning can reduce performance by up to about 10% in some cases.
Jeff found one of these cases.  While the autotuning penalty never exceeds
10% as far as I know, I can provide examples of other cases where autotuning
improves nfsd performance by more than a factor of 100.

The right thing is to fix autotuning.  If autotuning is considered too
broken to use, it should be turned off everywhere, not just in nfsd, as it
hurts/benefits all TCP clients, not just nfs.

This topic has been discussed before on netdev:
http://www.spinics.net/lists/netdev/msg68650.html
http://www.spinics.net/lists/netdev/msg68155.html
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