Re: [PATCH net-next 0/3] net: bcmgenet: collapse TX priority queues

[Nicolai Buchwitz <nb@tipi-net.de>]

Hi Jakub

On 13.6.2026 23:57, Jakub Kicinski wrote:
> On Fri, 12 Jun 2026 22:59:12 +0200 Nicolai Buchwitz wrote:
>> Tested on Raspberry Pi CM4 (BCM2711):
>>   - Ovidiu's reproducer (iperf3 -u -b0 -P16 -t60) no longer trips
>>     NETDEV_WATCHDOG.
>>   - UDP sustains 956 Mbit/s line rate over 60 s with 0 datagrams
>>     lost (0/4952890).
>>   - Single-stream TCP throughput unchanged at 943 Mbit/s.
> 
> Of course it has no impact on a single TCP stream test, since TCP
> stream can only use one queue. If anything it should help.
> The testing here is not very convincing. At least install a realistic
> qdisc (fq/fq_codel/cake) and run multi-stream test with multiple cores?
> What's the CPU idle delta in such a test?

Fair. Tests I ran with fq_codel:

   # TCP
   iperf3 -c <remote> -P 16
   # UDP
   iperf3 -c <remote> -u -b 1000M -P 16
   # RR
   iperf3 -c <remote> -t 60 &
   netperf -H <remote> -t TCP_RR -l 30 -- -r 1,1

With the following results (all based on net-next with PP):
                               PP       PP+WRR    PP+series
   TCP -P16 Mbit/s               938       941        941
   TCP retransmits             56228     57679      48606
   UDP -b1000M -P16 Mbit/s       956       956        956
   TCP_RR under TCP load       451.7     453.8      596.8
   CPU idle                    91.55%   90.53%     90.97%
   CPU0 softirq                32.6%    33.4%      33.5%
   CPU1-3 idle (avg)           97.6%    97.7%      97.7%

So WRR fixes the watchdog issue, otherwise is within noise. This series
adds ~31% TCP_RR under load and reduces retransmits by ~14%. Note, that
bcmgenet on BCM2711 has only two IRQs and no per-queue affinity, so all
HW interrupts are handled by one core regardless of queue count.

> 
> The reason for this change is not coming thru from the submission.
> Ovidiu's patch makes much more intuitive sense. I'll apply that,
> please rebase.

Will rebase and resend with a hopefully better reasoning :)

Thanks
Nicolai