When running refscale as a module, any ref_scale_init() issues will be
reflected in the error code from modprobe or insmod, as the case may be.
However, these error codes are not available when running refscale
built-in, for example, when using the kvm.sh script.  This commit
therefore adds WARN_ON_ONCE() to allow distinguishing ref_scale_init()
errors when running refscale built-in.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

This commit adds a "clock" type to refscale, which checks the performance
of ktime_get_real_fast_ns().  Use the "clocksource=" kernel boot parameter
to select the underlying clock source.

[ paulmck: Work around compiler false positive per kernel test robot. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

If the call to set_cpus_allowed_ptr() in ref_scale_reader()
fails, a later WARN_ONCE() complains.  But with the advent of
570a752b7a9b ("lib/smp_processor_id: Use is_percpu_thread() instead of
nr_cpus_allowed"), this complaint can be drowned out by complaints from
smp_processor_id().  The rationale for this change is that refscale's
kthreads are not marked with PF_NO_SETAFFINITY, which means that a system
administrator could change affinity at any time.

However, refscale is a performance/stress test, and the system
administrator might well have a valid test-the-test reason for changing
affinity.  This commit therefore changes to raw_smp_processor_id()
in order to avoid the noise, and also adds a WARN_ON_ONCE() to the
call to set_cpus_allowed_ptr() in order to directly detect immediate
failure.  There is no WARN_ON_ONCE() within the test loop, allowing
human-reflex-based affinity resetting, if desired.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

This commit adds scale_type of acqrel, lock, and lock-irq to
test acquisition and release.  Note that the refscale.nreaders=1
module parameter is required if you wish to test uncontended locking.
In contrast, acqrel uses a per-CPU variable, so should be just fine with
large values of the refscale.nreaders=1 module parameter.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

This commit adds a short delay for verbose_batched-throttled printk()s
to further decrease console flooding.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

The refscale test prints enough per-kthread console output to provoke RCU
CPU stall warnings on large systems.  This commit therefore allows this
output to be summarized.  For example, the refscale.verbose_batched=32
boot parameter would causes only every 32nd line of output to be logged.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

If an refscale torture-test run is given a bad kvm.sh argument, the
test will complain to the console, which is good.  What is bad is that
from the user's perspective, it will just hang for the time specified
by the --duration argument.  This commit therefore forces an immediate
kernel shutdown if a ref_scale_init()-time error occurs, thus avoiding
the appearance of a hang.  It also forces a console splat in this case
to clearly indicate the presence of an error.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

The default value for refscale.nreaders is -1, which results in the code
setting the value to three-quarters of the number of CPUs.  On single-CPU
systems, this results in three-quarters of the value one, which the C
language's integer arithmetic rounds to zero.  This in turn results in
a divide-by-zero error.

This commit therefore adds bounds checking to the refscale module
parameters, so that if they are less than one, they are set to the
value one.

Reported-by: kernel test robot <lkp@intel.com>
Tested-by "Chen, Rong A" <rong.a.chen@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Currently in the unlikely event that buf fails to be allocated it
is dereferenced a few times.  Use the errexit flag to determine if
buf should be written to to avoid the null pointer dereferences.

Addresses-Coverity: ("Dereference after null check")
Fixes: f518f154ecef ("refperf: Dynamically allocate experiment-summary output buffer")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

This commit further avoids conflation of refperf with the kernel's perf
feature by renaming kernel/rcu/refperf.c to kernel/rcu/refscale.c,
and also by similarly renaming the functions and variables inside
this file.  This has the side effect of changing the names of the
kernel boot parameters, so kernel-parameters.txt and ver_functions.sh
are also updated.

The rcutorture --torture type remains refperf, and this will be
addressed in a separate commit.

Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>