On Wed, Dec 18, 2024 at 11:51:26AM +1000, David Gwynne wrote:
>Hey Maurice,
>
>bluhm@ just did a talk at eurobsdcon that might help you understand the
>different points to look at. my tldr version is if packets are being
>dropped on the firewall it will be somewhere in the receive path. my
>experience is that once a packet has made it into the network stack
>it tends to get transmitted fine.
Thanks for your reply. This has given me some new things to look at.
>the places that packets can get dropped are in:
>
>1. hardware
>
>hardware counters from igc should be visible using kstat(1) now. the
>igc-stats that you're looking at would be any of the errs/colls, or the
>rx no bufs counter.
kstat(1) shows me that there are (nearly) no errors on the rx side, but
showed about 470k dropped packets (qdrops) on the tx side for igc2.
>2. rxq drops and errors
>
>the rxq is where packets received by the driver are put before being
>handed over to the network stack. again, these are visible as kstats,
>but are also aggregated as interface level counters you can see with
>netstat -i. you can look at drops and errors individiually with netstat
>-id and netstat -ie respectively.
netstat -id shows all zeros in de Idrop column, but the same 470k packets
in the Odrop column.
Not sure if this can also be caused by unplugging the cable. I did that
sereral times during testing/swapping switches on the igc2 port.
I will reboot to reset the counters and keep an eye on it.
>the fact that you're using pppoe on top of a vlan adds some potential
>for loss too. there's a queue in between ethernet input processing and
>pppoe processing that could be dropping packets. i don't think we have a
>way to see drops on that queue though.
>
>if you're feeling brave you can try the diff i sent to the 'PPPoE
>passthrough with "GigaHub" is very slow' thread on misc@ a week or so
>ago which skips the queue for pppoe data packets.
I think I can give it a try in a week or two.
For what it's worth: I see only 138 qdrops for pppoe0:0:txq:0 in kstat
output. And no drops on the rxq, but all counters are at zero so I guess
that doesn't say much.
>3. pf drops
>
>i think systat pf and pfctl -si are the best way to see counters here.
>however, i feel like there's some things that pf does and doesn't do
>sometimes that aren't captured well.
>
>4. tx drops
>
>again, i think this is unlikely, but you should be able to see tx
>interface drops using the txq kstats or drops/errors in netstat -i
>output. there's tx counters in the igc-stats too.
Furthermore, netstat -ss -p udp shows me:
udp:
295407643 datagrams received
1 with bad data length field
2100 with bad checksum
592550 with no checksum
289009064 input packets software-checksummed
318512247 output packets software-checksummed
25112 dropped due to no socket
239806 broadcast/multicast datagrams dropped due to no socket
431246 dropped due to full socket buffers
294709378 delivered
348403092 datagrams output
295132792 missed PCB cache
But I don't know if there dropped packets are also on igc2.
Thanks again and best regards,
Maurice
