Mats Liljegren <liljegren.ma...@gmail.com> writes:
> My company (Enea) wants to create test case(s) that verifies that you
> can run an application without having ticks going on the CPU that the
> application runs on. This would utilize the new nohz_full feature
> available from kernel version 3.10.
>
> I cannot find any existing test case in LTP in this area, so I assume
> I have to create the test case myself.
It's not in LTP, but I have a shell script[1] does some setup and load
generation that I use to validate nohz_full. The setup and
prerequisites can be a bit tricky, but some of the things it does:
- disables the residual 1Hz (if my patch is applied)
- pinning the unbound "writeback" workqueue to CPU0
- force timer migration using hotplug
- sets up CPUsets and tries to migrate all tasks to CPU0
(I think this part came from a script from you awhile ago)
It then uses 'stress' to generate load on specific CPUs and uses
trace-cmd to record the traces.
I currently look at the traces manually to see if it worked, but adding
other step to automatially look at the traces would be a good next step.
Kevin
[1]
#!/bin/bash
# Check that we have cpusets enabled in the kernel
if ! grep -q -s cpuset /proc/filesystems ; then
echo "Error: Kernel is lacking support for cpuset!"
exit 1
fi
# Try to disable sched_tick_max_deferment
if [ -e /sys/kernel/debug/sched_tick_max_deferment ]; then
echo -1 > /sys/kernel/debug/sched_tick_max_deferment
else
echo "WARNING: unable to set sched_tick_max_deferment"
fi
# if CONFIG_LOCKUP_DETECTOR is enabled, a periodic timer fires
# on *every* CPU, including idle ones. Disable it.
if [ -e /proc/sys/kernel/watchdog ]; then
echo 0 > /proc/sys/kernel/watchdog
fi
declare -a all_cpus=(`for file in /sys/devices/system/cpu/cpu*/online; do
basename $(dirname $file); done`)
declare -a cpus=( ${all_cpus[@]/cpu0/} ) # without CPU0
max_cpu=$((${#all_cpus[@]} - 1))
#
# Force migration off of NO_HZ CPUs using hotplug
# TODO: document what happens without this
#
for cpu in ${cpus[@]}; do
echo 0 > /sys/devices/system/cpu/$cpu/online
done
for cpu in ${cpus[@]}; do
echo 1 > /sys/devices/system/cpu/$cpu/online
done
# TODO: document what happens without this
# pin the writeback workqueue to CPU0
echo 1 > /sys/bus/workqueue/devices/writeback/cpumask
# make sure that the /dev/cpuset dir exits
# and mount the cpuset filesystem if needed
[ -d /dev/cpuset ] || mkdir /dev/cpuset
[ -e /dev/cpuset/tasks ] || mount -t cpuset none /dev/cpuset
# Create 2 cpusets. One GP and one NOHZ domain.
[ -d /dev/cpuset/gp ] || mkdir /dev/cpuset/gp
[ -d /dev/cpuset/rt ] || mkdir /dev/cpuset/rt
# Assume a single memory node
echo 0 > /dev/cpuset/gp/mems
echo 0 > /dev/cpuset/rt/mems
# Setup the GP domain: CPU0
echo 0 > /dev/cpuset/gp/cpus
# Setup the NOHZ domain: CPU1+
echo 1-$max_cpu > /dev/cpuset/rt/cpus
# Try to move all processes in top set to the GP set.
for pid in `cat /dev/cpuset/tasks`; do
if [ -d /proc/$pid ]; then
echo $pid > /dev/cpuset/gp/tasks 2>/dev/null
if [ $? != 0 ]; then
echo -n "Cannot move PID $pid: "
echo "$(cat /proc/$pid/status | grep ^Name | cut -f2)"
fi
fi
done
# Disable load balancing on top level (otherwise the child-sets' setting
# won't take effect.)
echo 0 > /dev/cpuset/sched_load_balance
# Enable load balancing withing the GP domain
echo 1 > /dev/cpuset/gp/sched_load_balance
#echo 1 > /dev/cpuset/rt/sched_load_balance
# But disallow load balancing within the NOHZ domain
echo 0 > /dev/cpuset/rt/sched_load_balance
DURATION=30
BACKOFF=$((DURATION / 8 * 1000000))
# Move self into GP domain
echo $$ > /dev/cpuset/gp/tasks
trace-cmd start -b 10000 -e sched -e irq -e timer -e signal
#trace-cmd start -b 100000 -e all
# GP domain
stress -q --cpu 2 --vm 2 --timeout $DURATION &
GP_PID=$!
# NOHZ domain
echo $$ > /dev/cpuset/rt/tasks || exit 1
# 2 temporarly overlapping tasks
stress -q --cpu 1 --timeout $[DURATION / 3] &
stress -q --cpu 1 --backoff $BACKOFF --timeout $[DURATION - 1] &
NOHZ_PID=$!
# start another busy task on the last CPU for >2 CPU machines
if [ $max_cpu > 1 ]; then
taskset -c $max_cpu stress -q --cpu 1 --timeout $DURATION &
fi
# Switch back to GP
echo $$ > /dev/cpuset/gp/tasks
# Wait for GP task(s) to finish
wait $GP_PID
trace-cmd stop
trace-cmd extract
sync
exit 0
#
# Cleanup
#
# Try to move all from GP back to root
for pid in `cat /dev/cpuset/gp/tasks`; do
if [ -d /proc/$pid ]; then
echo $pid > /dev/cpuset/tasks 2>/dev/null
if [ $? != 0 ]; then
echo -n "Cannot move PID $pid: "
echo "$(cat /proc/$pid/status | grep ^Name | cut -f2)"
fi
fi
done
# Remove the CPUsets
rmdir /dev/cpuset/gp
rmdir /dev/cpuset/rt
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