* Robin Holt <h...@sgi.com> wrote:
> We noticed that recently, reboot of a 1024 cpu machine takes approx 16
> minutes of just stopping the cpus. The slowdown was tracked to commit
> f96972f which went into v3.7 and then to the stable trees.
>
> x86 does not need to be running the boot cpu to pull reset and I don't
> think it is really needed for shutdown either.
>
> I decided to go the "simple" way and make this a config option that is
> selected by the x86 arch. I don't know which other arch's would also
> benefit, if any.
>
> Signed-off-by: Robin Holt <h...@sgi.com>
> To: Andrew Morton <a...@linux-foundation.org>
> Cc: Russ Anderson <r...@sgi.com>
> Cc: Thomas Gleixner <t...@linutronix.de>
> Cc: Ingo Molnar <mi...@redhat.com>
> Cc: "H. Peter Anvin" <h...@zytor.com>
> Cc: Shawn Guo <shawn....@linaro.org>
> Cc: <sta...@vger.kernel.org>
>
> ---
> arch/x86/Kconfig | 3 +++
> kernel/Kconfig.shutdown | 3 +++
> kernel/sys.c | 4 ++++
> 3 files changed, 10 insertions(+)
> create mode 100644 kernel/Kconfig.shutdown
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 70c0f3d..9611942 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -120,6 +120,7 @@ config X86
> select OLD_SIGSUSPEND3 if X86_32 || IA32_EMULATION
> select OLD_SIGACTION if X86_32
> select COMPAT_OLD_SIGACTION if IA32_EMULATION
> + select ARCH_SHUTDOWN_TO_ANY_CPU
>
> config INSTRUCTION_DECODER
> def_bool y
> @@ -839,6 +840,8 @@ config SCHED_MC
> making when dealing with multi-core CPU chips at a cost of slightly
> increased overhead in some places. If unsure say N here.
>
> +source "kernel/Kconfig.shutdown"
> +
> source "kernel/Kconfig.preempt"
>
> config X86_UP_APIC
> diff --git a/kernel/Kconfig.shutdown b/kernel/Kconfig.shutdown
> new file mode 100644
> index 0000000..d79fc04
> --- /dev/null
> +++ b/kernel/Kconfig.shutdown
> @@ -0,0 +1,3 @@
> +
> +config ARCH_SHUTDOWN_TO_ANY_CPU
> + bool
> diff --git a/kernel/sys.c b/kernel/sys.c
> index 39c9c4a..c0b8880 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -369,7 +369,9 @@ EXPORT_SYMBOL(unregister_reboot_notifier);
> void kernel_restart(char *cmd)
> {
> kernel_restart_prepare(cmd);
> +#ifndef CONFIG_ARCH_SHUTDOWN_TO_ANY_CPU
> disable_nonboot_cpus();
> +#endif
> if (!cmd)
> printk(KERN_EMERG "Restarting system.\n");
> else
> @@ -413,7 +415,9 @@ void kernel_power_off(void)
> kernel_shutdown_prepare(SYSTEM_POWER_OFF);
> if (pm_power_off_prepare)
> pm_power_off_prepare();
> +#ifndef CONFIG_ARCH_SHUTDOWN_TO_ANY_CPU
> disable_nonboot_cpus();
> +#endif
> syscore_shutdown();
> printk(KERN_EMERG "Power down.\n");
> kmsg_dump(KMSG_DUMP_POWEROFF);
Hm, the 'fix' is a pretty ugly workaround that does not fix much IMHO.
I think the original commit:
f96972f2dc63 kernel/sys.c: call disable_nonboot_cpus() in kernel_restart()
actually regressed your 1024 CPU systems, and should possibly be reverted or
fixed
in some other fashion - such as by migrating to the primary CPU (on
architectures
that require that), instead of hotplug offlining every secondary CPU on every
architecture!
Alternatively, disable_nonboot_cpus() could perhaps be improved to down CPUs in
parallel: issue the CPU-down requests to every CPU, then wait for them to
complete
- instead of the loop over every CPU?
This would be the conceptual counter part to parallel boot up of CPUs -
something
SGI might be interested in as well?
Thanks,
Ingo
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