Subject: Re: NAPI, e100, and system performance problem

From: jamal <[email-masked]>
Date: Mon, 18 Apr 2005 08:14:55 -0400

Jesse,

I doubt your problem has to do with interrupt rates.
If you say the CPU is "fast" - then the problem is elsewhere.
A fast machine that cant handle 77K interupt/sec would be a pathetic
one.
It could be the PCI IO rate which such a fast system shouldnt have
issues handling.
 
You say it can process upto two packets/interupt -so thats
pretty fast. Actually it could be the e100 issue - try replacing the NIC
with e1000 and repeat your tests and see if you observe the same
issues. 
If you are doing the netperf tests then collect netstat -s output;
/proc/net/softnet_stat is another useful stat to look at.

cheers,
jamal 

On Sun, 2005-17-04 at 23:11 -0700, Brandeburg, Jesse wrote:
> _Summary_
> As the part owner of the e100 driver, this issue has been nagging at me
> for a while.  NAPI seems to be able to swamp a system with interrupts
> and context switches.   In this case the system does not respond to
> having zero cpu cycles available by polling more, as I figured it would.
> This was mostly based on observation, but I included some quick data
> gathering for this mail.
>