Messages in this thread | | | From | Chris Friesen <> | Subject | question about isolcpus and nohz_full | Date | Thu, 9 Sep 2021 10:26:04 -0600 |
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Hi,
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 timer ticks.)
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?
Thanks,
Chris
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