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

[Jesper Dangaard Brouer <hawk@kernel.org>]

On 30/04/2026 11.45, Simon Schippers wrote:
> 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'

FYI: The selftest already tracks BQL "limit" and "inflight".
- Jonas can just report those BQL inflight logs

+print_periodic_stats() {
+    local elapsed="$1"
+
+    # BQL stats and watchdog counter
+    WD_CNT=$(cat /sys/class/net/${VETH_A}/queues/tx-0/tx_timeout \
+        2>/dev/null) || WD_CNT="?"
+    if [ -n "$BQL_DIR" ] && [ -d "$BQL_DIR" ]; then
+        INFLIGHT=$(cat "$BQL_DIR/inflight" 2>/dev/null || echo "?")
+        LIMIT=$(cat "$BQL_DIR/limit" 2>/dev/null || echo "?")
+        echo "  [${elapsed}s] BQL inflight=${INFLIGHT} limit=${LIMIT}" \
+            "watchdog=${WD_CNT}"
+    else
+        echo "  [${elapsed}s] watchdog=${WD_CNT} (no BQL sysfs)"
+    fi


> 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