Date: Mon, 12 Jan 2004 18:10:21 +0100 From: <gerald.heinig@ngi.de> To: hackers@freebsd.org Subject: ping duplicates under load Message-ID: <20040112172956.6368643D69@mx1.FreeBSD.org>
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Hi all, I've noticed a very weird phenomenon with ping which I can't explain. I have two machines with 2 NICs. When I started a ping -f with larger packet size (-s 3052) with NIC 1 and simultaneously hammered NIC 2 with UDP using ttcp, I got duplicate ping replies (on NIC 1, of course). Not many: only about 1 in 10000 to 100000, but still, I can't explain it. Since I had a similar problem a while back with another driver I developed (for OS X) and that turned out to be due to lost interrupts and my ISR not terminating quickly enough, I decided to limit the number of iterations of my ISR to 3. That improved the situation somewhat: I now only get 1 duplicate ping in 1E8. The real kicker is: I see this effect when my driver is the one doing the UDP receive. The ping duplicates also happen with other card drivers, so it's not a simple transmit/receive ring problem with my driver. When I use a different card driver to do the UDP receives, the effect goes away. It seems like the receive interrupt activity on my driver affects the ping replies of the _other_ drivers. Does anyone have any idea what could be going on? Cheers, Gerald
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