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The kernel thread executing test can run on any cpu, which might be
different cpu latency tracer is running on, as a result, the
big latency caused by preemptirq delay test can't be detected.
Therefore, the argument cpu_affinity is added to be passed to test,
ensure it's running on the same cpu with latency tracer.
e.g.
cyclictest -p 90 -m -c 0 -i 1000 -a 3
modprobe preemptirq_delay_test test_mode=preempt delay=500 \
burst_size=3 cpu_affinity=3
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Song Chen <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>
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A bug report was posted that running the preempt irq delay module on a slow
machine, and removing it quickly could lead to the thread created by the
modlue to execute after the module is removed, and this could cause the
kernel to crash. The fix for this was to call kthread_stop() after creating
the thread to make sure it finishes before allowing the module to be
removed.
Now this caused the opposite problem on fast machines. What now happens is
the kthread_stop() can cause the kthread never to execute and the test never
to run. To fix this, add a completion and wait for the kthread to execute,
then wait for it to end.
This issue caused the ftracetest selftests to fail on the preemptirq tests.
Link: https://lore.kernel.org/r/[email protected]
Cc: [email protected]
Fixes: d16a8c31077e ("tracing: Wait for preempt irq delay thread to finish")
Reviewed-by: Joel Fernandes (Google) <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>
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Running on a slower machine, it is possible that the preempt delay kernel
thread may still be executing if the module was immediately removed after
added, and this can cause the kernel to crash as the kernel thread might be
executing after its code has been removed.
There's no reason that the caller of the code shouldn't just wait for the
delay thread to finish, as the thread can also be created by a trigger in
the sysfs code, which also has the same issues.
Link: http://lore.kernel.org/r/[email protected]
Cc: [email protected]
Fixes: 793937236d1ee ("lib: Add module for testing preemptoff/irqsoff latency tracers")
Reported-by: Xiao Yang <[email protected]>
Reviewed-by: Xiao Yang <[email protected]>
Reviewed-by: Joel Fernandes <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>
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This burst feature enables the user to generate a burst of
preempt/irqsoff latencies. This makes it possible to test whether we
are able to detect latencies that systematically occur very close to
each other.
The maximum burst size is 10. We also create 10 identical test
functions, so that we get 10 different backtraces; this is useful
when we want to test whether we can detect all the latencies in a
burst. Otherwise, there would be no easy way of differentiating
between which latency in a burst was captured by the tracer.
In addition, there is a sysfs trigger, so that it's not necessary to
reload the module to repeat the test. The trigger will appear as
/sys/kernel/preemptirq_delay_test/trigger in sysfs.
Link: http://lkml.kernel.org/r/[email protected]
Reviewed-by: Joel Fernandes (Google) <[email protected]>
Signed-off-by: Viktor Rosendahl (BMW) <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>
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The preemptirq_delay_test module is used for the ftrace selftest code that
tests the latency tracers. The problem is that it uses ktime for the delay
loop, and then checks the tracer to see if the delay loop is caught, but the
tracer uses trace_clock_local() which uses various different other clocks to
measure the latency. As ktime uses the clock cycles, and the code then
converts that to nanoseconds, it causes rounding errors, and the preemptirq
latency tests are failing due to being off by 1 (it expects to see a delay
of 500000 us, but the delay is only 499999 us). This is happening due to a
rounding error in the ktime (which is totally legit). The purpose of the
test is to see if it can catch the delay, not to test the accuracy between
trace_clock_local() and ktime_get(). Best to use apples to apples, and have
the delay loop use the same clock as the latency tracer does.
Cc: [email protected]
Fixes: f96e8577da102 ("lib: Add module for testing preemptoff/irqsoff latency tracers")
Acked-by: Joel Fernandes (Google) <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>
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Automatically found by kbuild test robot.
Fixes: ffdc73a3b2ad ("lib: Add module for testing preemptoff/irqsoff latency tracers")
Signed-off-by: kbuild test robot <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>
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Here we introduce a test module for introducing a long preempt or irq
disable delay in the kernel which the preemptoff or irqsoff tracers can
detect. This module is to be used only for test purposes and is default
disabled.
Following is the expected output (only briefly shown) that can be parsed
to verify that the tracers are working correctly. We will use this from
the kselftests in future patches.
For the preemptoff tracer:
echo preemptoff > /d/tracing/current_tracer
sleep 1
insmod ./preemptirq_delay_test.ko test_mode=preempt delay=500000
sleep 1
bash-4.3# cat /d/tracing/trace
preempt -1066 2...2 0us@: preemptirq_delay_run <-preemptirq_delay_run
preempt -1066 2...2 500002us : preemptirq_delay_run <-preemptirq_delay_run
preempt -1066 2...2 500004us : tracer_preempt_on <-preemptirq_delay_run
preempt -1066 2...2 500012us : <stack trace>
=> kthread
=> ret_from_fork
For the irqsoff tracer:
echo irqsoff > /d/tracing/current_tracer
sleep 1
insmod ./preemptirq_delay_test.ko test_mode=irq delay=500000
sleep 1
bash-4.3# cat /d/tracing/trace
irq dis -1069 1d..1 0us@: preemptirq_delay_run
irq dis -1069 1d..1 500001us : preemptirq_delay_run
irq dis -1069 1d..1 500002us : tracer_hardirqs_on <-preemptirq_delay_run
irq dis -1069 1d..1 500005us : <stack trace>
=> ret_from_fork
Link: http://lkml.kernel.org/r/[email protected]
Cc: Boqun Feng <[email protected]>
Cc: Byungchul Park <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Julia Cartwright <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Paul McKenney <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Thomas Glexiner <[email protected]>
Cc: Todd Kjos <[email protected]>
Cc: Tom Zanussi <[email protected]>
Cc: Andy Shevchenko <[email protected]>
Reviewed-by: Andy Shevchenko <[email protected]>
[ Erick is a co-developer of this commit ]
Signed-off-by: Erick Reyes <[email protected]>
Signed-off-by: Joel Fernandes (Google) <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>
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