Re: [PATCH net-next 5/5] selftests: net: add veth BQL stress test

[Simon Schippers <simon.schippers@tu-dortmund.de>]

On 4/30/26 11:17, Jonas Köppeler wrote:
> On 3/28/26 4:19 PM, Simon Schippers wrote:
>> Hi, thanks for your work! I am really interested in this patchset.
>>
>> I am planning to submit a similar patch set (see [1]) for the tun/tap
>> driver, where I am currently implementing qdisc backpressure similar
>> to that used in veth.
>>
>> Can you run pktgen [2] to see if there is a regression?
>> I think that there might be a slowdown due to BQL not choosing a big
>> enough queue size.
> I ran some tests using pktgen by replacing the trafficgen from the
> selftest with samples/pktgen/pktgen_sample01_simple.sh (Patch v3)
> and used --nrules 0. In general the throughput is quite similar:
> 
> BQL disabled (using --bql-disable):
>   2378694pps 1141Mb/sec (1141773120bps) errors: 0
>   2400898pps 1152Mb/sec (1152431040bps) errors: 0
>   2358125pps 1131Mb/sec (1131900000bps) errors: 0
>   2402034pps 1152Mb/sec (1152976320bps) errors: 0
>   2362061pps 1133Mb/sec (1133789280bps) errors: 0
>   2416301pps 1159Mb/sec (1159824480bps) errors: 0
>   2398496pps 1151Mb/sec (1151278080bps) errors: 0
>   2415200pps 1159Mb/sec (1159296000bps) errors: 0
>   2375921pps 1140Mb/sec (1140442080bps) errors: 0
>   2427419pps 1165Mb/sec (1165161120bps) errors: 0
>   2382461pps 1143Mb/sec (1143581280bps) errors: 0
> 
>   mean: 2392510pps
> 
> BQL enabled:
>   2159545pps 1036Mb/sec (1036581600bps) errors: 0
>   2321899pps 1114Mb/sec (1114511520bps) errors: 0
>   2477853pps 1189Mb/sec (1189369440bps) errors: 0
>   2447857pps 1174Mb/sec (1174971360bps) errors: 0
>   2400284pps 1152Mb/sec (1152136320bps) errors: 0
>   2442841pps 1172Mb/sec (1172563680bps) errors: 0
>   2442540pps 1172Mb/sec (1172419200bps) errors: 0
>   2410585pps 1157Mb/sec (1157080800bps) errors: 0
>   2395902pps 1150Mb/sec (1150032960bps) errors: 0
>   2393260pps 1148Mb/sec (1148764800bps) errors: 0
>   2401959pps 1152Mb/sec (1152940320bps) errors: 0
> 
>   mean: 2390411pps
> 
> BQL enabled is ~2099pps (~0.09%) lower than BQL disabled.

Sounds great!

One more thing:
Could you check what BQL limit settles during the test run using
something like:

watch -n 0.1 'cat /sys/class/net/XXXXX/queues/tx-0/byte_queue_limits/limit'

I guess it will just choose the ptr_ring size as limit in this case,
but it would be nice if you could briefly verify this :)

Thanks!

> 
>> Thanks!
>>
>> [1] Link:https://lore.kernel.org/all/20260312130639.138988-1-simon.schippers@tu-dortmund.de/
>> [2] Link:https://www.kernel.org/doc/html/latest/networking/pktgen.html