question about isolcpus and nohz_full
From: Chris Friesen
Date: Thu Sep 09 2021 - 12:26:13 EST
I'm finally getting around to moving to a newer kernel, and I'm running
into a warning "Housekeeping: nohz_full= must match isolcpus=".
In my environment I had a number of "fully-isolated" CPUs with both
"isolcpus" and "nohz_full", then a number of less-isolated CPUs that had
"nohz_full" enabled but not "isolcpus", then the housekeeping CPUs. It
appears this is no longer supported via the boot args. (The
"less-isolated CPUs were used for applications that expected the usual
load balancing from the scheduler but didn't want to be interrupted by
1) The kernel-parameters documentation for "isolcpus=" doesn't say
anything about needing to match "nohz_full", nor does the documentation
for "nohz_full" mention that it needs to align with "isolcpus". Maybe
this would be a good thing to add?
2) Is it allowed to specify "nohz_full" for some CPUs at boot time
without specifying any isolcpus? If so, what happens if I later isolate
a subset of those CPUs using "cpuset.sched_load_balance" in cgroups? Is
that allowed when the equivalent boot args are not?