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Re: NAPI interrupt data

To: jamal <hadi@xxxxxxxxxx>
Subject: Re: NAPI interrupt data
From: Jeff Garzik <jgarzik@xxxxxxxxx>
Date: Sat, 15 Feb 2003 13:55:46 -0500
Cc: netdev@xxxxxxxxxxx, linux-net@xxxxxxxxxxxxxxx
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jamal wrote:

On Sat, 15 Feb 2003, Jeff Garzik wrote:


bash-2.05b$ ./x.pl data.crumb
135 samples, 21578 avg
bash-2.05b$ ./x.pl data.hum
130 samples, 11213 avg



Probably the first 5-10 samples as well as the last 5-10 amples to get
more accuracy.

This data looks fine, no?

Over 4000 interrupts per second was not something I was hoping for, to be honest. ttcp did not even report 50% CPU utilization, so I reach the conclusion that both machines can handle well in excess of 4,000 interrupts per second... but overall I do not like the unbounded nature of the interrupt rate. This data makes me lean towards a software[NAPI] + hardware mitigation solution, as opposed to totally depending on software interrupt mitigation.


> definetly the scsi device is skewing things
(you are writting data to disk for example).

Yes, though only once 5 seconds when ext3 flushes. With nothing else going on but "ttcp" and "cat /proc/interrupts >> data ; sleep 1" there should be very little disk I/O. I agree it is skewing by an unknown factor, however.


- The 500Kpps from ttcp doesnt sound right; tcp will slow you down.
perhaps use ttcp to send udp packets to get a more interesting view.


No, I ran 500,000 buffer I/Os total from ttcp ("-n 500000"). That doesn't really say anything about packets per second. The only thing I measured was interrupts per second. It was my mistake to type "packets" in the first email :/

        Jeff




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