Hi Sebastian,
On 14.06.25 10:52, Marc Strämke wrote:
I do not really understand where the IRQ/Preemption disabling is
happening. What would the next thing be to do? Function (graph?)
tracing on all the functions visible in the backtrace?
I tried to look at the event race output starting with the call to
igb_set_rx_mode. I have attached the trace with all events and a
function filter on igb on only the cpu executing ip. I cannot
understand what is happening between timestasmp 700.149995 and the IRQ
disable event on 700.150795....
Thanks for your help,
Marc
I am still trying to figure that puzzle out: Please see the following
function trace snippet:
ip-690530 [000] ..... 178636.460435: rtnl_is_locked <-__dev_change_flags
ip-690530 [000] ..... 178636.460435: __local_bh_disable_ip
<-__dev_change_flags
ip-690530 [000] ..... 178636.460435: migrate_disable
<-__local_bh_disable_ip
ip-690530 [000] ...1. 178636.460435: preempt_disable:
caller=__local_bh_disable_ip+0x76/0xe0
parent=__local_bh_disable_ip+0x76/0xe0
ip-690530 [000] ...11 178636.460435: preempt_enable:
caller=__local_bh_disable_ip+0x76/0xe0
parent=__local_bh_disable_ip+0x76/0xe0
ip-690530 [000] ....1 178636.460435: rt_spin_lock <-__local_bh_disable_ip
ip-690530 [000] ....1 178636.460436: __rcu_read_lock <-rt_spin_lock
ip-690530 [000] ....1 178636.460436: migrate_disable
<-__local_bh_disable_ip
ip-690530 [000] ....2 178636.460436: __rcu_read_lock
<-__local_bh_disable_ip
ip-690530 [000] b...2 178636.460436: rt_spin_lock <-__dev_change_flags
ip-690530 [000] b...2 178636.460436: __rcu_read_lock <-rt_spin_lock
ip-690530 [000] b...2 178636.460436: migrate_disable <-__dev_change_flags
ip-690530 [000] b...3 178636.460436: __dev_set_rx_mode <-__dev_change_flags
ip-690530 [000] b...3 178636.460437: igb_set_rx_mode <-__dev_change_flags
It is my understanding that __local_bh_disable_ip called from
netif_addr_lock_bh seems to be the origin of my latency.
What i do not understand is, even if the bottom halves are disabled.
Shouldn't I see the interrupt arriving in the trace?
If i understood it correctly, your talk "Unblocking the softirq lock for
PREEMPT_RT" during the plumbers conference 2023 is exactly about that
case, right?
Probably fixing this issue is out of my abilities for now ;-) The wast
variety of locking concepts inside the kernel is quite intimidating for
a newcomer in kernel land...
Regards,
Marc
