On Fri, Jan 17, 2020 at 12:16 PM Rob Landley [off-list ref] wrote:

On 1/14/20 5:06 AM, Hsin-Yi Wang wrote:

quoted

This patch adds a config ARCH_OFFLINE_CPUS_ON_REBOOT, which would offline cpus in
migrate_to_reboot_cpu(). If non reboot cpus are all offlined here, the loop for
checking online cpus would be an empty loop. If architecture don't enable this
config, or some cpus somehow fails to offline, it would fallback to ipi
function.

I'm curious:

quoted

+# Select to do a full offline on secondary CPUs before reboot.
+config ARCH_OFFLINE_CPUS_ON_REBOOT
+     bool "Support for offline CPUs before reboot"
+     depends on HOTPLUG_CPU

The new symbol can't be selected without the other symbol.

quoted

+     select ARCH_OFFLINE_CPUS_ON_REBOOT if HOTPLUG_CPU

And the other symbol automatically selects the new one.

Why are you adding a second symbol that means the same thing as the existing symbol?

I should make the arch selecting this symbol in other patches and let
the arch decides if they want to opt in, as Thomas pointed out in v5:
https://lore.kernel.org/lkml/8736cgxmxi.fsf@nanos.tec.linutronix.de/ (local)

Current solution is not sufficient since it only solve problems for
system that enables HOTPLUG_CPU.

quoted

+#if defined(CONFIG_PM_SLEEP_SMP) || defined(CONFIG_ARCH_OFFLINE_CPUS_ON_REBOOT)
+extern int freeze_secondary_cpus(int primary, bool reboot);
+#endif

Couldn't that just test HOTPLUG_CPU? What's the second symbol for? (You can have
empty stub functions when architectures don't support a thing...)

Rob

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