On Wed, 7 Oct 2009, rihad wrote:

rihad wrote:
I've yet to test how this direct=0 improves extensive dummynet drops.

Ooops... After a couple of minutes, suddenly:

net.inet.ip.intr_queue_drops: 1284

Bumped it up a bit.

Yes, I was going to suggest that moving to deferred dispatch has probably simply moved the drops to a new spot, the queue between the ithreads and the netisr thread. In your setup, how many network interfaces are in use, and what drivers?

If what's happening is that you're maxing out a CPU then moving to multiple netisrs might help if your card supports generating flow IDs, but most lower-end cards don't. I have patches to generate those flow IDs in software rather than hardware, but there are some downsides to doing so, not least that it takes cache line misses on the packet that generally make up a lot of the cost of processing the packet.

My experience with most reasonable cards is that letting them doing the work distribution with RSS and use multiple ithreads is a more performant strategy than using software work distribution on current systems, though.

Someone has probably asked for this already, but -- could you send a snapshot of the top -SH output in the steady state? Let top run for a few minutes and then copy/paste the first 10-20 lines into an e-mail.

Robert N M Watson
Computer Laboratory
University of Cambridge
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