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Date:	Mon, 11 Aug 2014 16:50:15 +0800
From:	Lan Tianyu <tianyu.lan@...el.com>
To:	ego@...ux.vnet.ibm.com
CC:	rjw@...ysocki.net, len.brown@...el.com, pavel@....cz,
	peterz@...radead.org, toshi.kani@...com, mingo@...nel.org,
	akpm@...ux-foundation.org, todd.e.brandt@...ux.intel.com,
	fabf@...net.be, srivatsa.bhat@...ux.vnet.ibm.com,
	rafael.j.wysocki@...el.com, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org
Subject: Re: [RFC PATCH] PM/CPU: Parallel enabling nonboot cpus with resume
 devices

On 2014年08月08日 18:55, Gautham R Shenoy wrote:
> 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 <tianyu.lan@...el.com>
>> ---
>>  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.
> 

Hi Gautham:

Great thanks for your review. Yes, you are right. I will take it into
account when send out V2.

> 
>> +
>> +	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.
> 


-- 
Best regards
Tianyu Lan
--
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