Re: Why is em nic generating interrupts?

----- Original Message -----
From: "Terry Lambert" <tlambert2_at_mindspring.com>
To: "Michael O. Boev" <mike_at_tric.tomsk.gov.ru>; "Terry Lambert"
<tlambert2_at_mindspring.com>
Cc: <freebsd-current_at_FreeBSD.ORG>
Sent: Saturday, October 11, 2003 3:54 AM
Subject: RE: Why is em nic generating interrupts?


> Michael O. Boev wrote:
> > From: Terry Lambert [mailto:tlambert2_at_mindspring.com]
> > > "Michael O. Boev" wrote:
> > > > I've got a [uniprocessor 5.1-RELEASE] router machine with fxp
> > > > and em nics.
> > > > I've built my kernel with the following included:
> > > >
> > > > options         DEVICE_POLLING
> > > > options         HZ=2500
> > > >
> > > > and enabled polling in /etc/sysctl.conf.
> > > [ ... ]
> > > > What's happening? Is polling working in my case?
> > > > If yes, why is vmstat showing interrupts? I see clearly,
> > > > that fxp's counter doesn't increase, and em's is constantly growing.
> > > >
> > > > Is there anyone who knows for sure that em's polling works?
> > >
> > > You may want to ask Luigi; polling is his code.
> > >
> > > However, I believe the issue is that polling doesn't start
> > > until you take an interrupt, and it stops as soon as there is
> > > no more data to process, and waits for the next interrupt.
> > >
> > > If you were to jack your load way up, you would probably see
> > > an increase in interrupts, then them dropping off dramatically.
> > To this dare I object, that there is traffic going through this machine,
> > and fxp0 is NOT generating interrupts, while em IS. So, if the rule
above
> > works, they both have to behave in same ways.
>
> This is the third time I've received this message.  I guess you feel some
> urgency about receiving a reply?
Oh, no )). I even didn't send it for 3 times. Sorry for annoyance.
>
> My answer is this:  I did the polling code for a number of the drivers,
and
> though it was committed by someone else, I can guarantee you that it
> will have interrupts, unless the code was implemented incorreectly, since
> the code is meant to  do this polling only under heavy load.
I believe you... I just wondered why two drivers behaved differently.

...
> If your FXP is not generating any interrupts at all, i think that the
polling
> code in it is probably broken.
>
> Note: I believe this might be one of the ones I modified, since Luigi's
code
> originally only dealt with Gigabit NICs, though I may be mistaken.  If so,
> my statement that it's broken should be considered to be pretty
> authoritative.  8-).
Then, OK, it is now fxp's polling that probably behaves oddly :)). Since
I've ever
been only using fxps, I got used to this behaviour. Thus my questions.
>
> -- Terry
>
Thanks for thorough explanations!

Mike.