fxp performance with POLLING

Chuck Swiger cswiger at mac.com
Fri Oct 3 18:02:43 UTC 2008

Pieter de Goeje wrote:
> On Friday 03 October 2008, Bartosz Stec wrote:
>> Hello again :)
>> With POLLING enabled I experience about 10%-25% performance drop when
>> copying files over network. Tested with both SAMBA and NFS. Is it normal?
> Yes. You don't want to use polling unless you set kern.hz to 10000 or 
> something in that range.

HZ = 1000 or 2000 is fine for most purposes, at least up through T3 level 
bandwidth.  For a home LAN or small business office of a half-dozen machines 
using DSL/Cable (~ 1-5 MBs up), even a P2-300 or VIA C3 600 at HZ=250 works OK 
as a firewall/router.  The main thing that using polling does is that it adds 
a reasonably fixed amount of latency (ie, the poll interval) but gives solid 
processing performance even under heavy load, just as you say:

> If you have a NIC with interrupt moderation, polling 
> should almost never be necessary. Note that polling can still be useful for 
> routers, because it allows you to have a much more responsive system even 
> when handling heavy network traffic.

Note that he's got the link0 flag going, so that should mean he's using 
firmware with the fxp NIC which does interrupt moderation.


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