Messages in this thread | | | From | Hsin-Yi Wang <> | Date | Tue, 14 Jan 2020 01:00:48 +0800 | Subject | Re: [PATCH RFC v3 1/3] reboot: support hotplug CPUs before reboot |
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On Mon, Jan 13, 2020 at 11:57 PM Vitaly Kuznetsov <vkuznets@redhat.com> wrote: > > Hsin-Yi Wang <hsinyi@chromium.org> writes: > > > On Mon, Jan 13, 2020 at 8:46 PM Vitaly Kuznetsov <vkuznets@redhat.com> wrote: > > > > Thanks for your comments. > > > >> > +config REBOOT_HOTPLUG_CPU > >> > + bool "Support for hotplug CPUs before reboot" > >> > + depends on HOTPLUG_CPU > >> > + help > >> > + Say Y to do a full hotplug on secondary CPUs before reboot. > >> > >> I'm not sure this should be a configurable option, e.g. in case this is > >> a good approach in general, why not just use CONFIG_HOTPLUG_CPU in the > >> code? > >> > > In v2 it uses CONFIG_HOTPLUG_CPU, but I think adding another config is > > more flexible. Maybe there are some architecture that supports > > HOTPLUG_CPU but doesn't want to do full cpu hotplug before reboot. > > (Eg. doing cpu hotplug would make reboot process slower.) > > In that case this should be an architectural decision, not a selectable > option. If you want to enable it for certain arches only (and not the > other way around), that would look like > > config ARCH_HAS_HOTUNPLUG_CPUS_ON_REBOOT > bool > > ... > > config X86 > def_bool y > ... > select ARCH_HAS_HOTUNPLUG_CPUS_ON_REBOOT > > because as a user, I really have no idea if I want to 'unplug secondary > CPUs on reboot' or not. > Thanks for the example. I would use this way in next version. > >> > + > >> > config HAVE_OPROFILE > >> > bool > >> > > >> > diff --git a/include/linux/cpu.h b/include/linux/cpu.h > >> > index 1ca2baf817ed..3bf5ab289954 100644 > >> > --- a/include/linux/cpu.h > >> > +++ b/include/linux/cpu.h > >> > @@ -118,6 +118,9 @@ extern void cpu_hotplug_disable(void); > >> > extern void cpu_hotplug_enable(void); > >> > void clear_tasks_mm_cpumask(int cpu); > >> > int cpu_down(unsigned int cpu); > >> > +#if IS_ENABLED(CONFIG_REBOOT_HOTPLUG_CPU) > >> > +extern void offline_secondary_cpus(int primary); > >> > +#endif > >> > > >> > #else /* CONFIG_HOTPLUG_CPU */ > >> > > >> > diff --git a/kernel/cpu.c b/kernel/cpu.c > >> > index 9c706af713fb..52afc47dd56a 100644 > >> > --- a/kernel/cpu.c > >> > +++ b/kernel/cpu.c > >> > @@ -1057,6 +1057,25 @@ int cpu_down(unsigned int cpu) > >> > } > >> > EXPORT_SYMBOL(cpu_down); > >> > > >> > +#if IS_ENABLED(CONFIG_REBOOT_HOTPLUG_CPU) > >> > +void offline_secondary_cpus(int primary) > >> > +{ > >> > + int i, err; > >> > + > >> > + cpu_maps_update_begin(); > >> > + > >> > + for_each_online_cpu(i) { > >> > + if (i == primary) > >> > + continue; > >> > + err = _cpu_down(i, 0, CPUHP_OFFLINE); > >> > + if (err) > >> > + pr_warn("Failed to offline cpu %d\n", i); > >> > + } > >> > + cpu_hotplug_disabled++; > >> > + > >> > + cpu_maps_update_done(); > >> > +} > >> > +#endif > >> > >> This looks like a simplified version of freeze_secondary_cpus(), can > >> they be merged? > >> > > Comparing to freeze_secondary_cpus(), I think it's not necessary to > > check pm_wakeup_pending() before _cpu_down() here. Thus it doesn't > > need to depend on CONFIG_PM_SLEEP_SMP. > > Also I think it could continue to offline other CPUs even one fails, > > while freeze_secondary_cpus() would stop once it fails on offlining > > one CPU. > > Based on these differences, I didn't use freeze_secondary_cpus() here. > > As for merging the common part, it might need additional flags to > > handle the difference, which might lower the readability. > > I have to admit I'm not convinced (but maintainers may disagree of > course): #ifdefs are there to avoid compiling code which we don't need, > in case a second user emerges we can drop them or #ifdef just some parts > of it, it's not set in stone. Also, in case the only difference is that > you don't want to stop if some CPU fails to offline, a single bool flag > (e.g. 'force') would solve the problem, I don't see a significant > readability change. > Okay, I will merge them with an additional flag for whether it should check pm_wakeup_pending() and break on error. > -- > Vitaly >
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