Hi Lan,
On Wed, Jul 23, 2014 at 05:11:34PM +0800, Lan Tianyu wrote:
> In the current world, all nonboot cpus are enabled serially during system
> resume. System resume sequence is that boot cpu enables nonboot cpu one by
> one and then resume devices. Before resuming devices, there are few tasks
> assigned to nonboot cpus after they are brought up. This waste cpu usage.
>
> To accelerate S3, this patches adds a new kernel configure
> PM_PARALLEL_CPU_UP_FOR_SUSPEND to allow boot cpu to go forward to resume
> devices after bringing up one nonboot cpu. The nonboot cpu will be in charge
> of bringing up other cpus. This makes enabling cpu2~x parallel with resuming
> devices. From the test result on 4 logical core laptop, the time of resume
> device almost wasn't affected by enabling nonboot cpus lately while the start
> point is almost 30ms earlier than before.
>
> Signed-off-by: Lan Tianyu <[email protected]>
> ---
> kernel/cpu.c | 82
> ++++++++++++++++++++++++++++++++++++++++++++++------
> kernel/power/Kconfig | 13 +++++++++
> 2 files changed, 86 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index a343bde..d4c1353 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -551,9 +551,27 @@ void __weak arch_enable_nonboot_cpus_end(void)
> {
> }
>
> +static int _cpu_up_with_trace(int cpu)
> +{
> + int error;
> +
> + trace_suspend_resume(TPS("CPU_ON"), cpu, true);
> + error = _cpu_up(cpu, 1);
> + trace_suspend_resume(TPS("CPU_ON"), cpu, false);
> + if (error) {
> + pr_warn("Error taking CPU%d up: %d\n", cpu, error);
> + return error;
> + }
> +
> + pr_info("CPU%d is up\n", cpu);
> + return 0;
> +}
> +
[..snip..]
>
> +
> +void __ref enable_nonboot_cpus(void)
> +{
> + struct task_struct *tsk;
> + int cpu;
> +
> + /* Allow everyone to use the CPU hotplug again */
> + cpu_maps_update_begin();
> + cpu_hotplug_disabled = 0;
> + if (cpumask_empty(frozen_cpus))
> + goto out;
> +
> + arch_enable_nonboot_cpus_begin();
> +
> + cpu = cpumask_first(frozen_cpus);
> + cpumask_clear_cpu(cpu, frozen_cpus);
> +
> + _cpu_up_with_trace(cpu);
We should be handling the error returned by _cpu_up_with_trace()
in case 'cpu' fails to come online. Unless it is something that I am
not aware of it doesn't make much sense to create a kthread on a cpu
that we know has failed to come online.
> +
> + if (cpumask_empty(frozen_cpus)) {
> + arch_enable_nonboot_cpus_end();
> + } else {
> + tsk = kthread_create_on_cpu(async_enable_nonboot_cpus,
> + NULL, cpu, "async-enable-nonboot-cpus");
> + if (IS_ERR(tsk)) {
> + pr_err("Failed to create async enable nonboot cpus
> thread.\n");
> + goto out;
> + }
> +
> + kthread_unpark(tsk);
> + }
> +out:
> + cpu_maps_update_done();
> +}
> +#endif
> +
--
Thanks and Regards
gautham.
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