Messages in this thread | | | Subject | Re: question about isolcpus and nohz_full | From | Mike Galbraith <> | Date | Fri, 10 Sep 2021 06:14:43 +0200 |
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On Thu, 2021-09-09 at 10:26 -0600, Chris Friesen wrote: > > 2) Is it allowed to specify "nohz_full" for some CPUs at boot time > without specifying any isolcpus?
Yup (IM[not the least bit;]HO the proper way to partition a box).
> 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?
That's what an old shield script I still have laying around does. I booted master on my little desktop box with nohz_full=1,2,3,5,6,7 and shielded cores 2 and 3, after taking down cpus 4-7 (smt), and it still seems to work fine.
I used to also override (via ugly.. maybe even fugly, hack) nohz dynamically, turning the tick on/off for subsets, on having proven best for jitter of heftily threaded RT app spread across many isolated cores, thus could at need even partition a box with a mixture of ticked, nohz idle, and tickless sets, albeit in a rather limited fashion due to nohz_full preallocation requirement. Would be nice for some situations if nohz mode were to become a fully dynamic set attribute.
-Mike
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