On Fri, May 03, 2019 at 10:47:37AM -0700, tip-bot for Nicholas Piggin wrote: > Commit-ID: 9219565aa89033a9cfdae788c1940473a1253d6c > Gitweb: https://git.kernel.org/tip/9219565aa89033a9cfdae788c1940473a1253d6c > Author: Nicholas Piggin <npiggin@xxxxxxxxx> > AuthorDate: Thu, 11 Apr 2019 13:34:47 +1000 > Committer: Ingo Molnar <mingo@xxxxxxxxxx> > CommitDate: Fri, 3 May 2019 19:42:58 +0200 > > sched/isolation: Require a present CPU in housekeeping mask > > During housekeeping mask setup, currently a possible CPU is required. > That does not guarantee the CPU would be available at boot time, so > check to ensure that at least one present CPU is in the mask. I have a doubt about the requirements and semantics of cpu_present_mask. IIUC a present CPU means that it is physically plugged in (from ACPI perspective) but might not be logically plugged in (set on cpu_online_mask). But do we have the guarantee that a present CPU _will_ be online at least once right after the boot? After all, kernel parameters such as "maxcpus=" can prevent from turning some CPUs on. I guess there are even more creative ways to achieve that. In any case we really require the housekeeper to be forced online. Perhaps I missed that enforcement somewhere in the patchset? Thanks.
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