[Soekris] high CPU usage for network interrupts on 4801
ml.janhoevers at xs4all.nl
Sun Sep 16 21:15:16 UTC 2007
Trevor Talbot wrote on 16-9-2007 22:26:
>> I've tried downloading a large file to the NTP machine at a much
>> higher speed (6800 kbit/sec), which takes about 75% CPU for interrupt
>> processing. I guess the small size of NTP packets is inefficient.
> Yes, figures like 40Mbps are a "best case" scenario with full-size
> packets. With small packets, the limiting factor is packets per
> second, as each one incurs processing.
Ok, I understand. No 40 Mbps of NTP traffic can be expected. My upstream
connection wouldn't handle that anyway.
But I assume that downloading a 100 Mb file by FTP involves full size
>> However, this 75% is stil much higher than I would expect.
> That seems a bit high to me too. What are the other 5 ethernet ports
Four of them doing nothing (unplugged for the occasion). The last one
carrying two ssh sessions to monitor the top displays. Traffic nothing
really compared to the NTP packets flowing.
>> I've tried moving the NTP machine from an ethernet port on the 1641 to
>> one on the 4801 board in an attempt to avoid the PCI bus, but it makes
>> little or no difference. (Maybe I'm not avoiding the PCI bus this way,
>> I'm not sure.)
> You're not, it all goes over the PCI bus either way.
Ok, that's clear too.
> I'll let others cover FreeBSD specifically, since I haven't done any
> testing with recent versions. One thing that would help is getting a
> handle on what pps rates you're actually seeing, though. I don't know
> if pfsense measures it, but you can get an idea with:
> netstat -I sis0 -w 1
I believe something like 1500 pps, plus 1500 replies going the other
way, but it's a guess. I hope to get back to you with some measurement,
but I'll have to wait for the next burst.
Thanks for answering,
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