On Wed, Aug 18, 2010 at 11:49:39PM -0700, David Miller wrote:

From: Jarek Poplawski <redacted>
Date: Sun, 15 Aug 2010 22:04:31 +0200

quoted

I've just tested it using a simplistic patch below, which skips
some napi receiving by doing it only every second jiffie (on even
ones), and I've got around 30% less interrupts from via-rhine,
which seems to suggest napi works OK, but there is too low
traffic (or too fast soft interrupt handling) to affect hard
interrupts. (Btw, probably CONFIG_HZ can matter here a bit too.
I tested with 1000.)

100Mbit on any modern system isn't going to trigger NAPI much at all
even with near full link utilization.

The simply cpu processes the packets too fast for them to gather up
much at all.

Some improvement in polling could be gained if the via-rhine has some
HW interrupt mitigation settings.  However after a quick perusal of
the driver I don't see anything about this.  The mitigation ethtool
ops aren't implemented either, so I'm not optimistic :-)

Yes, now I see the old comments (pre 2.6.27) mentioned 10kpps
threshold, which wasn't reached in Jakub's example.

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=32b0f53e5bc80b87fd20d4d78a0e0cb602c9157a

Jarek P.