I'm seeing some very strange interrupt behavior in 2.2.0 when using a 4Mbps
IrDA/IrLAN connection. For some traffic, TCP performance is really bad. The
strange thing is that it performs _much_ better if I give the machine
interrupts of some kind. Holding down the space key, or moving the mouse
will do. The configuration TCP <-> IrLAN <-> IrDA <-> PC87108 will then
perform much better, but when I release the space key, performance is
really bad again.
The problem seems to be related to the drivers/net/irda/pc87108.c
driver. The driver worked really fine using 2.0 kernels and up to about
2.1.131 (I think). The pc87108 uses DMA for both tx and rx so I don't know
why more interrupts will make the work DMA better (I get fewer rx fifo
overruns when I hold down the space key). Rx dma is enabled before the
first frame arrives, so interrupt latency shouldn't have anything to do
with it. The machine used is a Pentium 200.
One other problem is that the esound daemon (esd) gives so many interrupts
(about 300/s) that using the serial driver is impossible. Just gets a lot
of fifo rx overruns. Making ppp connect is just impossible, but when I kill
esd, ppp works just fine again (same for irda drivers).
I'm sorry I that I can't tell you more than just the symptoms, but I don't
really have a clue of whats going on! Anybody that can give me some hints?
-- Dag
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