Slow disk write speeds over network

Hiten Pandya hmp at
Wed Jun 11 18:03:50 PDT 2003

On Wed, Jun 11, 2003 at 03:19:10AM -0700, Terry Lambert wrote:
> > Ok - done.. some where defaults, and I couldn't find net.isr.enable..
> > Did I need to config something on my kernel for it to show up?
> You have to set a compile option; look in /usr/src/sys/net; grep
> for "netisr_dispatch" or just "dispatch".


	``NetISR Dispatch'' and friends are not available in
	FreeBSD 4.x versions.  I am sure that he is using 4.x and
	that's why he can't find it in his source.

> The net.isr.enable=1 will save you about 100ms per packet,
> minimum, and more if you have a high interrupt overhead that
> livelocks you from running NETISR.  What it does is turns on
> direct processing by IP and TCP of packets as they come in
> the interface and you get the interrupt.  Combined with soft
> interrupt coelescing and polling, they should  give you
> another 1/3 of the receiver livelock fixup.  The final third
> isn't available, unless you are willing to hack network stack
> code and scheduler code, since FreeBSD doesn't include LRP or
> Weighted Fair Share Queuing.

	Does it help if queueing discipline is changed?

> > which should be good enough cards to support it.. I've also put 100Mbit
> > cards in place of the gige's for now to make sure I wasn't hitting a
> > GigE problem or negotiation problem..
> You should grep for DEVICE_POLLING in the network device
> drivers you are interested in using to see if they have the
> support.  Also you can get up to 15% by adding soft interrupt
> coelescing code, if the driver doesn't already support it (I
> added it for a couple of drivers, and it was committed after
> the benchmarks showed it was good, but it's not everywhere);
> the basic idea is you take the interrupt, run rx_eof(), and
> call ether_input().  Then repeat the process until you hit
> some count limit, or until there's no more data.  The direct
> dispatch (net.isr.enable) combined with that will process most
> packet trains to completion at interrupt, saving you 10ms up
> and 10ms back down per packet exchange (NETISR only runs on
> exit from spl or at the HZ time, which is default every 10ms).
	Hmm, can you point these drivers to me?

		-- Hiten (hmp at FreeBSD.ORG)

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