Re: NetBSD 5.1 TCP performance issue (lots of ACK)

[David Young <dyoung%pobox.com@localhost>]

On Mon, Nov 21, 2011 at 10:11:17PM +0100, Manuel Bouyer wrote:
> On Mon, Nov 21, 2011 at 02:58:57PM -0600, Greg Oster wrote:
> > Hi Manuel
> > 
> > Have there been issues with these patches that prevent them from being
> > applied to -current and/or pulled up?
> 
> Nothing wrong AFAIK, I just got distracted.
> 
> > (says he who saw reasonably
> > abysmal network performance this weekend on a bunch of machines with
> > wm0 in use, and would like to see some better performance.)
> 
> But it would be good to test these patches on different hardware
> or with different applications :)

The changes to interrupt-mitigation made performance worse with the
82573: the CPU saturates at a lower packet rate with the patch than
without.

It looks to me like wm(4) tries to throttle receive interrupts using two
different methods simultaneously.  One method is RDTR + RADV, and the
other is ITR.  It seems to me that the driver should pick one method
based on the product and use that method exclusively.

In the manual for the 82573, Intel recommends ITR instead of RDTR+RADV
(as opposed to ITR in addition to RDTR+RADV).  I think that we should
follow the manual.

I see that wm(4) tries to throttle transmit interrupts, too.  I think
that the driver would be simpler, and it would perform no worse, if it
did not request transmit interrupts.  Just reclaim transmitted buffers
in the if_start routine and in an if_drain routine.

Dave

-- 
David Young
dyoung%pobox.com@localhost    Urbana, IL    (217) 721-9981