Userspace starving kernel threads for CPU cycle.

[Àbéjídé Àyodélé]

The short answer:  'man 7 sched'

Thanks I read this and I think I might still be confused. I am using cgroups
and have cpu.cfs_quota_us configured as 2300000 and cpu.cfs_period_us
configured as 100000 for 3 different cgroups of, all of these I assume
equates
69 cpus along with a couple of other cgroups with cpu.cfs_quota_us
configured
on a 80 cpu machine which is why I made my original guess.

The first question is, of course: "Did you see any actual evidence of kernel
threads being starved?"

I have a couple of very similar machines with similar workloads and observed
the below type of messages in dmesg on several of them:

rcu_sched detected stalls on CPUs
Sending NMI from CPU 43 to CPUs 14
watchdog: BUG: soft lockup - CPU#26 stuck for 22s [migration/54:335]
ixgbe 0000:19:00.1 eno2: initiating reset due to tx timeout

Which is why I have this hypothesis.

I am still unclear if the cgroup group controller makes guarantees such that
tasks in the cgroup cannot be preempted even if a kernel thread requires cpu
time.

Thanks for your time!

Abejide Ayodele
It always seems impossible until it's done. --Nelson Mandela
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