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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-DetectorID-Processed: b00c1d49-9d2e-4205-b15f-d015386d3d5e On 10/16/26 05:18, 'Eugen Hristev' via BCM-KERNEL-FEEDBACK-LIST,PDL wrote: > Limit each iProc MSI parent IRQ to 16 event-queue entries. > > A continuously fed queue could otherwise keep the chained handler running > and starve other work. The budget still drains pending events and lets the > next parent interrupt continue processing, improving fairness and bounding > interrupt-handler latency. > > Without this starvation avoidance, one CPU can stall indefinitely > in the loop and not serve other interrupts, timers, etc. > > While testing it with an Ethernet NIC, when too many MSI interrupts > come in, CPU might get starved: > > Connecting to host 192.168.30.1, port 5201 > [ 5] local 192.168.30.2 port 52586 connected to 192.168.30.1 port 5201 > [ ID] Interval Transfer Bitrate Retr Cwnd > [ 5] 0.00-1.00 sec 240 MBytes 2.01 Gbits/sec 2 334 KBytes > [ 5] 1.00-2.00 sec 63.2 MBytes 531 Mbits/sec 1 1.41 KBytes > [ 5] 2.00-3.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes > [ 5] 3.00-4.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes > [ 5] 4.00-5.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes > [ 5] 5.00-6.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes > [ 5] 6.00-7.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes > [ 5] 7.00-8.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes > [ 5] 8.00-9.00 sec 0.00 Bytes 0.00 bits/sec 0 1.41 KBytes > [ 177.568497] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: > [ 177.568913] rcu: 0-...!: (1 GPs behind) idle=28ac/1/0x4000000000000002 softirq=28922/28930 fqs=1 > [ 177.569457] rcu: (detected by 1, t=5256 jiffies, g=21629, q=819 ncpus=4) > [ 177.569870] Sending NMI from CPU 1 to CPUs 0: > > With this bounded approach, IRQ handler will complete and continue > to serve MSI events on the next handler invocation. > > Assisted-by: Github Copilot > Signed-off-by: Eugen Hristev Reviewed-by: Florian Fainelli -- Florian