[c-nsp] lots of input errors & ignored

[Rodney Dunn]

You are filling up the rx ring and depelting the fifo buffers to the
chipset before the processor can service that rx_interrupt.
That's the most common cause of ignores on a software switching
platform.

What is th rx_ring depth in 'sh controllers'? I bet it's 64.

We've had to bump it up to 128 on some platforms that have
GIGE access to accomondate micro burst on the wire.

Having flow control support would help some but I don't think this
chipset supports it.

At the average rates below you have a lot of room for 
burst but the 7401 without PXF is, IIRC, the speed of a 
NPE300 which isn't all that fast.

Maybe get a sniffer trace and see what the real burst speed
on the wire is?

The only thing you might could tune is the scheduler allocate
to give more cycles to interrupt if you don't have a lot
of process traffic/work to do. 

The default is usually a 20:1 ratio. Try setting it to 40:1 or
so and see if it helps.

Rodney

On Wed, Jul 25, 2007 at 11:06:47AM +0200, Philippe Strauss wrote:
> Hello c-nsp,
> 
> I have a c7401 running c7400-is-mz.124-13b.bin with "no ip pxf" acting
> as an ADSL LNS showing high rate on one of it's interface of "input errors"
> and "ignored". It comes in burst, not incrementing during one minute or so,
> then during ~10 seconds, it increase of 20 to 1000 packets!
> overall, it's near 1% input packet dropped.
> Usually (as the doco says at least) it's related to buffers, but I can't
> see the "show buffers" output increamenting ("misses" values) for any sized
> buffers, nor in the Fa1/0 private particle buffers.
> sh controller fa1/0 gives the exact same number as "ignored" under "RX No Buff".there's a rate limit to 10Mbps in/out on this interface, but
> "show int fa1/0 rate" gives very different numbers.
> 
> rt-cc-lns1#sh int fa1/0
> FastEthernet1/0 is up, line protocol is up
>   Hardware is i82543 (Livengood), address is 000b.fcc4.d81c (bia 000b.fcc4.d81c)
>   Description: ADSL Home
>   Internet address is 195.70.20.18/30
>   MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
>      reliability 255/255, txload 4/255, rxload 21/255
>   Encapsulation ARPA, loopback not set
>   Keepalive set (10 sec)
>   Full-duplex, 100Mb/s, 100BaseTX/FX
>   ARP type: ARPA, ARP Timeout 04:00:00
>   Last input 00:00:06, output 00:00:00, output hang never
>   Last clearing of "show interface" counters 01:08:11
>   Input queue: 0/75/34/0 (size/max/drops/flushes); Total output drops: 0
>   Queueing strategy: fifo
>   Output queue: 0/40 (size/max)
>   5 minute input rate 8294000 bits/sec, 1052 packets/sec
>   5 minute output rate 1856000 bits/sec, 769 packets/sec
>      3965119 packets input, 3548670736 bytes
>      Received 0 broadcasts, 0 runts, 0 giants, 12 throttles
>      27965 input errors, 0 CRC, 0 frame, 0 overrun, 27965 ignored <--- !!!!!!!
>      0 watchdog
>      0 input packets with dribble condition detected
>      2751492 packets output, 909061474 bytes, 0 underruns
>      0 output errors, 0 collisions, 0 interface resets
>      0 babbles, 0 late collision, 0 deferred
>      0 lost carrier, 0 no carrier
>      0 output buffer failures, 0 output buffers swapped out
> 
> regards.
> 
> -- 
> Philippe Strauss
> av. de Beaulieu 25
> 1004 Lausanne
> http://philou.ch
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