Messages in this thread | | | Date | Fri, 6 Apr 2007 12:47:04 -0500 | From | Nathan Lynch <> | Subject | Re: [PATCH 3/8] Use process freezer for cpu-hotplug |
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Ingo Molnar wrote: > > * Nathan Lynch <ntl@pobox.com> wrote: > > > > - raw_notifier_call_chain(&cpu_chain, CPU_LOCK_ACQUIRE, hcpu); > > > + if (freeze_processes(FE_HOTPLUG_CPU)) { > > > + thaw_processes(FE_HOTPLUG_CPU); > > > + return -EBUSY; > > > + } > > > + > > > > If I'm understanding correctly, this will cause > > > > # echo 0 > /sys/devices/system/cpu/cpuX/online > > > > to sometimes fail, and userspace is expected to try again? This will > > break existing applications. > > > > Perhaps drivers/base/cpu.c:store_online should retry as long as > > cpu_up/down return -EBUSY. That would avoid a userspace-visible > > interface change. > > yeah. I'd even suggest a freeze_processes_nofail() API instead, that > does this internally, without burdening the callsites. (and once the > freezer becomes complete then freeze_processes_nofail() == > freeze_processes())
Yeah, I just realized that an implementation of my proposal would busy loop in the kernel forever if a silly admin tried to offline the last cpu (we're already using -EBUSY for that case), so freeze_processes_nofail is a better idea :-)
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