On 2/18/21 4:12 PM, Sebastian Andrzej Siewior wrote:
On 2020-12-30 14:09:19 [+0100], Jonathan Schwender wrote:
Hi everyone,
I've been trying to test the real-time `performance` possible with
containers, by running cyclictest in a container on an RT-Kernel.
The issue I've been having does not require containers or an
RT kernel though.
Issue: cyclictest freezes after running for a few seconds
to minutes. After that only the loadavg section is updated,
while the count line does not change anymore.
cyclictest can't be killed after that point
other than by restarting the machine, and
this also takes a few minutes until the kernel kills
cyclictest.
This behaviour only occurs when the following conditions are
met:
- RT_GROUP_SCHED is used
- cyclictest is bound to an isolated cpu core with
nohz_full=<core>, and isolcpus=nohz,domain,<core>
So if you remove RT_GROUP_SCHED and use cyclictest on the nohz_full
cores then everything is fine?
Yes, I traced it down to RT throttling breaking if nohz_full is set and
a non-root cgroup is used.
The timer tick which resets the runtime, gets moved to a housekeeping
CPU, which
doesn't service the isolated CPUs. This leads to the task being RT
throttled indefinitely.
I proposed a patch [1] which solved my issue however, I haven't received
any feedback on it yet.
The patch basically just extends the exception for the root cgroup to
also apply to all housekeeping CPUs,
but I assume there are better ways to fix this that I don't know about.
[1]
https://lore.kernel.org/lkml/20210202090010.5350-1-schwenderjonathan@xxxxxxxxx/
Sebastian
Jonathan
