Dropped packets on SUN GEM

[Beezly <beezly@beezly.org.uk>]

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Hi David,

I've been running some more tests on the GEM card. It seems to be
recovering from the RX hangs ok, but when I ping another host on the
network (with a .1s interval).. I get the following


monkey:/home/andy# ping -s 1472 -i .1 10.0.0.15
PING 10.0.0.15 (10.0.0.15) from 10.0.0.12 : 1472(1500) bytes of data.
1480 bytes from 10.0.0.15: icmp_seq=1 ttl=255 time=0.586 ms
1480 bytes from 10.0.0.15: icmp_seq=2 ttl=255 time=0.554 ms
1480 bytes from 10.0.0.15: icmp_seq=3 ttl=255 time=0.561 ms
1480 bytes from 10.0.0.15: icmp_seq=4 ttl=255 time=0.565 ms
<snip>
1480 bytes from 10.0.0.15: icmp_seq=570 ttl=255 time=0.557 ms
1480 bytes from 10.0.0.15: icmp_seq=571 ttl=255 time=0.550 ms
1480 bytes from 10.0.0.15: icmp_seq=572 ttl=255 time=0.558 ms
1480 bytes from 10.0.0.15: icmp_seq=573 ttl=255 time=0.552 ms
1480 bytes from 10.0.0.15: icmp_seq=574 ttl=255 time=0.558 ms
1480 bytes from 10.0.0.15: icmp_seq=575 ttl=255 time=0.570 ms
1480 bytes from 10.0.0.15: icmp_seq=590 ttl=255 time=0.565 ms
1480 bytes from 10.0.0.15: icmp_seq=591 ttl=255 time=0.562 ms
1480 bytes from 10.0.0.15: icmp_seq=592 ttl=255 time=0.567 ms
1480 bytes from 10.0.0.15: icmp_seq=593 ttl=255 time=0.526 ms
1480 bytes from 10.0.0.15: icmp_seq=594 ttl=255 time=0.560 ms
1480 bytes from 10.0.0.15: icmp_seq=595 ttl=255 time=0.562 ms

notice the missing 14 packets.

Now, if I reproduce the test with a .2s interval between pings, I get
the following results.

monkey:/home/andy# ping -s 1472 -i .2 10.0.0.15
PING 10.0.0.15 (10.0.0.15) from 10.0.0.12 : 1472(1500) bytes of data.
1480 bytes from 10.0.0.15: icmp_seq=1 ttl=255 time=0.645 ms
1480 bytes from 10.0.0.15: icmp_seq=2 ttl=255 time=0.578 ms
1480 bytes from 10.0.0.15: icmp_seq=3 ttl=255 time=0.592 ms
1480 bytes from 10.0.0.15: icmp_seq=4 ttl=255 time=0.585 ms
1480 bytes from 10.0.0.15: icmp_seq=5 ttl=255 time=0.575 ms
1480 bytes from 10.0.0.15: icmp_seq=6 ttl=255 time=0.577 ms
<snip>
1480 bytes from 10.0.0.15: icmp_seq=292 ttl=255 time=0.564 ms
1480 bytes from 10.0.0.15: icmp_seq=293 ttl=255 time=0.559 ms
1480 bytes from 10.0.0.15: icmp_seq=294 ttl=255 time=0.568 ms
1480 bytes from 10.0.0.15: icmp_seq=295 ttl=255 time=0.561 ms
1480 bytes from 10.0.0.15: icmp_seq=310 ttl=255 time=0.588 ms
1480 bytes from 10.0.0.15: icmp_seq=311 ttl=255 time=0.568 ms
1480 bytes from 10.0.0.15: icmp_seq=312 ttl=255 time=0.572 ms
1480 bytes from 10.0.0.15: icmp_seq=313 ttl=255 time=0.576 ms
1480 bytes from 10.0.0.15: icmp_seq=314 ttl=255 time=0.569 ms

notice, 14 missing packets again. 

I'm pretty confident (as confident I can be whilst doing a "watch -n1
ifconfig"!) that it's doing this *during* the RX hang recovery, so it
appears that the RX hang recovery is taking 15 packets-worth of time,
rather than a set period of time (as I would expect - incorrectly?). 

Is this normal? - Because it seems the amount of time to recover from a
hang is inversely proportional to the amount of work it is doing, I am
able to artificially improve the "uptime" of the card by permanantly
running a ping -f <host> on the box!!

Cheers,

Beezly



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