Messages in this thread | | | Subject | Re: [PATCH 3/8] Use process freezer for cpu-hotplug | From | Nigel Cunningham <> | Date | Sat, 07 Apr 2007 08:22:35 +1000 |
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Hi.
On Fri, 2007-04-06 at 12:47 -0500, Nathan Lynch wrote: > 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 :-)
If there's only one online cpu, shouldn't it return -EINVAL?
Regards,
Nigel
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