Hi,
what and how does the latency_hist/preemptirqsoff measure?
The ftrace.txt says
"preemptirqsoff"
Similar to irqsoff and preemptoff, but traces and
records the largest time for which irqs and/or preemption
is disabled.
# head -3 /sys/kernel/debug/tracing/latency_hist/wakeup/CPU0
#Minimum latency: 8 microseconds
#Average latency: 15 microseconds
#Maximum latency: 95 microseconds
# head -3 /sys/kernel/debug/tracing/latency_hist/timerandwakeup/CPU0
#Minimum latency: 8 microseconds
#Average latency: 15 microseconds
#Maximum latency: 95 microseconds
# head -3 /sys/kernel/debug/tracing/latency_hist/wakeup/sharedprio/CPU0
#Minimum latency: 9 microseconds
#Average latency: 42 microseconds
#Maximum latency: 603 microseconds (this is OK, there are such threads)
# head -3 /sys/kernel/debug/tracing/latency_hist/irqsoff/CPU0
#Minimum latency: 0 microseconds
#Average latency: 2 microseconds
#Maximum latency: 136 microseconds
# head -3 /sys/kernel/debug/tracing/latency_hist/preemptoff/CPU0
#Minimum latency: 2 microseconds
#Average latency: 7 microseconds
#Maximum latency: 121 microseconds
# head -6 /sys/kernel/debug/tracing/latency_hist/preemptirqsoff/CPU0
#Minimum latency: 0 microseconds
#Average latency: 2 microseconds
#Maximum latency: 29001 microseconds
#Total samples: 29054669
#There are 0 samples lower than 0 microseconds.
#There are 15 samples greater or equal than 10240 microseconds.
The 29 ms looks bogus. There are two test-applications running
and each one would cry loudly being without CPU for 10 ms or more.
Or is there a possibility that the irqsoff and preemptoff alternate
so that everything looks normal but there is not a single time
both are possible?
3.4.25-rt37, preempt full.
Thanks
--
Stano
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