We are seeing nonrt behavior with GPIO interrupts using the sysfs
interface. We setup the pin by setting the ".../edge" file to
"rising", and then use epoll to wait for a priority event on the
".../value" file.
>From turning on the IRQ trace events, the workqueue trace events, and
the scheduler trace events, it looks like the sysfs event goes through
a workqueue, which is SCHED_OTHER.
<idle>-0 [000] d..h2.. 9739.478875: irq_handler_entry:
irq=103 name=48057000.gpio
<idle>-0 [000] d..h2.. 9739.478877: irq_handler_exit:
irq=103 ret=handled
<idle>-0 [000] d..h3.. 9739.478879: sched_waking:
comm=irq/103-4805700 pid=105 prio=26 target_cpu=000
<idle>-0 [000] dn.h4.. 9739.478884: sched_wakeup:
comm=irq/103-4805700 pid=105 prio=26 target_cpu=000
<idle>-0 [000] d...3.. 9739.478892: sched_switch:
prev_comm=swapper/0 prev_pid=0 prev_prio=120 prev_state=R ==>
next_comm=irq/103-4805700 next_pid=105 next_prio=26
irq/103-4805700-105 [000] d...211 9739.478904: irq_handler_entry:
irq=135 name=gpiolib
irq/103-4805700-105 [000] d...211 9739.478906: irq_handler_exit:
irq=135 ret=handled
irq/103-4805700-105 [000] d...311 9739.478909: sched_waking:
comm=irq/135-gpiolib pid=3380 prio=26 target_cpu=001
irq/103-4805700-105 [000] d...411 9739.478914: sched_wakeup:
comm=irq/135-gpiolib pid=3380 prio=26 target_cpu=001
<idle>-0 [001] d...3.. 9739.478919: sched_switch:
prev_comm=swapper/1 prev_pid=0 prev_prio=120 prev_state=R ==>
next_comm=irq/135-gpiolib next_pid=3380 next_prio=26
irq/135-gpiolib-3380 [001] ....115 9739.478928:
workqueue_queue_work: work struct=c0a6c944
function=kernfs_notify_workfn workqueue=ef0c1300 req_cpu=2 cpu=1
irq/135-gpiolib-3380 [001] ....115 9739.478930:
workqueue_activate_work: work struct c0a6c944
irq/135-gpiolib-3380 [001] d...315 9739.478932: sched_waking:
comm=kworker/1:1 pid=3168 prio=120 target_cpu=001
irq/103-4805700-105 [000] d...3.. 9739.478934: sched_switch:
prev_comm=irq/103-4805700 prev_pid=105 prev_prio=26 prev_state=S ==>
next_comm=swapper/0 next_pid=0 next_prio=120
irq/135-gpiolib-3380 [001] d...415 9739.478937: sched_wakeup:
comm=kworker/1:1 pid=3168 prio=120 target_cpu=001
irq/135-gpiolib-3380 [001] d...3.. 9739.478951: sched_switch:
prev_comm=irq/135-gpiolib prev_pid=3380 prev_prio=26 prev_state=S ==>
next_comm=kworker/1:1 next_pid=3168 next_prio=120
kworker/1:1-3168 [001] ....1.. 9739.478957:
workqueue_execute_start: work struct c0a6c944: function
kernfs_notify_workfn
kworker/1:1-3168 [001] d...213 9739.478962: sched_waking:
comm=gps_main pid=3374 prio=26 target_cpu=001
kworker/1:1-3168 [001] dn..313 9739.478967: sched_wakeup:
comm=gps_main pid=3374 prio=26 target_cpu=001
kworker/1:1-3168 [001] dn..313 9739.478970: sched_stat_runtime:
comm=kworker/1:1 pid=3168 runtime=17731 [ns] vruntime=138492205643
[ns]
kworker/1:1-3168 [001] d...313 9739.478974: sched_switch:
prev_comm=kworker/1:1 prev_pid=3168 prev_prio=120 prev_state=R+ ==>
next_comm=gps_main next_pid=3374 next_prio=26
gps_main-3374 [001] d...411 9739.478983: sched_pi_setprio:
comm=kworker/1:1 pid=3168 oldprio=120 newprio=26
gps_main-3374 [001] d...311 9739.478994: sched_switch:
prev_comm=gps_main prev_pid=3374 prev_prio=26 prev_state=D ==>
next_comm=kworker/1:1 next_pid=3168 next_prio=26
kworker/1:1-3168 [001] d...313 9739.479000: sched_waking:
comm=gps_main pid=3374 prio=26 target_cpu=001
kworker/1:1-3168 [001] d...413 9739.479003: sched_wakeup:
comm=gps_main pid=3374 prio=26 target_cpu=001
kworker/1:1-3168 [001] d...313 9739.479006: sched_pi_setprio:
comm=kworker/1:1 pid=3168 oldprio=26 newprio=120
kworker/1:1-3168 [001] d...313 9739.479010: sched_stat_runtime:
comm=kworker/1:1 pid=3168 runtime=1952 [ns] vruntime=138492207595 [ns]
kworker/1:1-3168 [001] dn..313 9739.479015: sched_stat_runtime:
comm=kworker/1:1 pid=3168 runtime=4555 [ns] vruntime=138492212150 [ns]
kworker/1:1-3168 [001] d...313 9739.479018: sched_switch:
prev_comm=kworker/1:1 prev_pid=3168 prev_prio=120 prev_state=R+ ==>
next_comm=gps_main next_pid=3374 next_prio=26
gps_main-3374 [001] ....1.. 9739.479032: sys_epoll_wait -> 0x1
gps_main-3374 [001] ....1.. 9739.479033: sys_exit: NR 252 = 1
For our use case, we were able to switch to the PPS driver, but I
thought it worthwhile to raise this in case anyone else runs across
it. Is this a known issue?
Thanks,
Austin
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