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SubjectRe: [patch] x86: avoid unnecessary smp alternatives switch during suspend/resume
Hi.

On 20/11/10 11:09, Suresh Siddha wrote:
> During suspend, we disable all the non boot cpus. And during resume we bring
> them all back again. So no need to do alternatives_smp_switch() in between.
>
> This speeds up both suspend and resume paths.
>
> Signed-off-by: Suresh Siddha<suresh.b.siddha@intel.com>
> ---
>
> arch/x86/kernel/smpboot.c | 7 ++++++-
> include/linux/cpu.h | 2 ++
> kernel/cpu.c | 3 +++
> 3 files changed, 11 insertions(+), 1 deletions(-)
>
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index f0a0624..0b04ca3 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -1349,7 +1349,12 @@ void native_cpu_die(unsigned int cpu)
> if (system_state == SYSTEM_RUNNING)
> pr_info("CPU %u is now offline\n", cpu);
>
> - if (1 == num_online_cpus())
> + /*
> + * Don't do the smp alternatives switch during
> + * suspend. We will be back in the SMP mode after
> + * resume.
> + */
> + if (1 == num_online_cpus()&& !pm_sleep_smp)
> alternatives_smp_switch(0);
> return;
> }
> diff --git a/include/linux/cpu.h b/include/linux/cpu.h
> index 4823af6..8cab04c 100644
> --- a/include/linux/cpu.h
> +++ b/include/linux/cpu.h
> @@ -169,11 +169,13 @@ static inline void cpu_hotplug_driver_unlock(void)
>
> #ifdef CONFIG_PM_SLEEP_SMP
> extern int suspend_cpu_hotplug;
> +extern int pm_sleep_smp;
>
> extern int disable_nonboot_cpus(void);
> extern void enable_nonboot_cpus(void);
> #else /* !CONFIG_PM_SLEEP_SMP */
> #define suspend_cpu_hotplug 0
> +#define pm_sleep_smp 0
>
> static inline int disable_nonboot_cpus(void) { return 0; }
> static inline void enable_nonboot_cpus(void) {}
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 8615aa6..2eed810 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -381,6 +381,7 @@ out:
>
> #ifdef CONFIG_PM_SLEEP_SMP
> static cpumask_var_t frozen_cpus;
> +int pm_sleep_smp;
>
> int disable_nonboot_cpus(void)
> {
> @@ -393,6 +394,7 @@ int disable_nonboot_cpus(void)
> * with the userspace trying to use the CPU hotplug at the same time
> */
> cpumask_clear(frozen_cpus);
> + pm_sleep_smp = 1;
>
> printk("Disabling non-boot CPUs ...\n");
> for_each_online_cpu(cpu) {
> @@ -454,6 +456,7 @@ void __ref enable_nonboot_cpus(void)
>
> cpumask_clear(frozen_cpus);
> out:
> + pm_sleep_smp = 0;
> cpu_maps_update_done();
> }
We have a few others things that want to modify their behaviour
according to whether we're doing the atomic copy/restore. Perhaps it
would be an idea to just use a single flag, perhaps a value for
system_state?

Nigel


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