Hi,
using cyclictest I measure long max latencies of >10ms on a Wandboard
dual (Freescale i.MX6 dual Cortex-A9 SoC).
The latency problem happens with diffent scenarios:
- without or with rt-patch (4.1.7-rt8 w. CONFIG_PREEMPT_RT_FULL)
- different Kernels (3.17, 4.1, 4.2 w. CONFIG_PREEMPT__LL)
- different CPU governors including 'performance'
- independant of CPU load
- even with no other userspace processes but init, the login sh and
cyclictest (I use a minimal builroot rfs).
- independant of cyclictest prio
Using the same buildroot rfs on a A20 SoC (bananapro) with 4.1.7-rt8
shows acceptable rt-latencies of ~ 200us.
Ftracing 'irqsoff' on the rt-patched 4.1 kernel shows always long
latency after 'raw_spin_lock_irq' (see log below).
Do you think it is a driver which stalls or hrtimer not working
correctly on this SoC or someting else?
If it is a driver, how could I find out which it is?
Thanks
Matthias
------------------------------------------
Test log with 4.1.7-rt8 kernel and no additional load:
# cyclictest --smp -p98 -m
# /dev/cpu_dma_latency sepolicy: fifo: loadavg: 3.66 3.87 3.61 4/87 580
WARN: Running on unknown kernel version...YMMV
T: 0 ( 572) P:98 I:1000 C:1225776 Min: 52 Act: 317 Avg: 393
Max: 6161
T: 1 ( 573) P:98 I:1500 C: 816449 Min: 64 Act: 143 Avg: 381
Max: 4567
# cat trace
# tracer: irqsoff
#
# irqsoff latency trace v1.1.5 on 4.1.7-rt8-wb+
# --------------------------------------------------------------------
# latency: 4062 us, #7/7, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:2)
# -----------------
# | task: cyclictest-338 (uid:0 nice:0 policy:1 rt_prio:95)
# -----------------
# => started at: _raw_spin_lock_irq
# => ended at: _raw_spin_unlock_irq
#
#
# _--------=> CPU#
# / _-------=> irqs-off
# | / _------=> need-resched
# || / _-----=> need-resched_lazy
# ||| / _----=> hardirq/softirq
# |||| / _---=> preempt-depth
# ||||| / _--=> preempt-lazy-depth
# |||||| / _-=> migrate-disable
# ||||||| / delay
# cmd pid |||||||| time | caller
# \ / |||||||| \ | /
sh-156 0dn..111 1us#: trace_hardirqs_off <-_raw_spin_lock_irq
cyclicte-338 0d...3.. 4052us : finish_task_switch <-__schedule
cyclicte-338 0d...3.. 4057us : _raw_spin_unlock_irq <-finish_task_switch
cyclicte-338 0d...3.. 4059us : do_raw_spin_unlock <-_raw_spin_unlock_irq
cyclicte-338 0d...2.. 4061us : trace_hardirqs_on <-_raw_spin_unlock_irq
cyclicte-338 0d...2.. 4066us+: time_hardirqs_on <-_raw_spin_unlock_irq
cyclicte-338 0d...2.. 4080us : <stack trace>
=> trace_hardirqs_on
=> _raw_spin_unlock_irq
=> finish_task_switch
=> __schedule
=> schedule
=> do_nanosleep
=> __hrtimer_nanosleep
=> hrtimer_nanosleep
=> common_nsleep
=> SyS_clock_nanosleep
=> ret_fast_syscall
#
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