linux-kernel - Re: [RFC PATCH V2] PM/CPU: Parallel enalbing nonboot cpus with resume devices

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Message-ID: <54011932.4060405@intel.com>
Date:	Sat, 30 Aug 2014 02:22:10 +0200
From:	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
To:	Lan Tianyu <tianyu.lan@...el.com>, peterz@...radead.org,
	mingo@...nel.org, srivatsa@....edu, akpm@...ux-foundation.org,
	laijs@...fujitsu.com, toshi.kani@...com,
	todd.e.brandt@...ux.intel.com, wangyun@...ux.vnet.ibm.com,
	ego@...ux.vnet.ibm.com, fabf@...net.be, linux@....linux.org.uk
CC:	oleg@...hat.com, srivatsa.bhat@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH V2] PM/CPU: Parallel enalbing nonboot cpus with resume
 devices

On 8/29/2014 5:40 AM, Lan Tianyu wrote:
> On 2014年08月22日 16:33, 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 allows 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.
>>
>> Signed-off-by: Lan Tianyu <tianyu.lan@...el.com>
>> ---
>> Change since V1:
>> 	Remove PM_PARALLEL_CPU_UP_FOR_SUSPEND kernel config and make
>> paralleling cpu as default behaviour. Add error handling for
>> failure of the first frozen cpu online.
>>
>> So far, I just tested the patch on the Intel machines. It's better
>> to test it on the others Arch platforms. Appreciate a lot if some
>> one can help test it.
>>
> Hi All:
> 	Any comments on this patch?  Thanks.

You need to ensure that the async thing completes before 
cpufreq_resume() or bad things will happen I think.

>>   kernel/cpu.c | 70 +++++++++++++++++++++++++++++++++++++++++++++++++-----------
>>   1 file changed, 58 insertions(+), 12 deletions(-)
>>
>> diff --git a/kernel/cpu.c b/kernel/cpu.c
>> index a343bde..9bc8497 100644
>> --- a/kernel/cpu.c
>> +++ b/kernel/cpu.c
>> @@ -551,8 +551,42 @@ void __weak arch_enable_nonboot_cpus_end(void)
>>   {
>>   }
>>   
>> +static int _cpu_up_with_trace(int cpu)

Better name?

>> +{
>> +	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;
>> +}
>> +
>> +static int async_enable_nonboot_cpus(void *data)
>> +{
>> +	int cpu;
>> +
>> +	cpu_maps_update_begin();
>> +	arch_enable_nonboot_cpus_begin();

Shouldn't you call this before trying to bring up the first one?

>> +
>> +	for_each_cpu(cpu, frozen_cpus) {
>> +		_cpu_up_with_trace(cpu);
>> +	}
>> +
>> +	arch_enable_nonboot_cpus_end();
>> +	cpumask_clear(frozen_cpus);
>> +	cpu_maps_update_done();
>> +	return 0;
>> +}
>> +
>>   void __ref enable_nonboot_cpus(void)
>>   {
>> +	struct task_struct *tsk;
>>   	int cpu, error;
>>   
>>   	/* Allow everyone to use the CPU hotplug again */
>> @@ -563,22 +597,34 @@ void __ref enable_nonboot_cpus(void)
>>   
>>   	pr_info("Enabling non-boot CPUs ...\n");
>>   
>> -	arch_enable_nonboot_cpus_begin();
>> +	cpu = cpumask_first(frozen_cpus);
>> +	cpumask_clear_cpu(cpu, frozen_cpus);
>>   
>> -	for_each_cpu(cpu, frozen_cpus) {
>> -		trace_suspend_resume(TPS("CPU_ON"), cpu, true);
>> -		error = _cpu_up(cpu, 1);
>> -		trace_suspend_resume(TPS("CPU_ON"), cpu, false);
>> -		if (!error) {
>> -			pr_info("CPU%d is up\n", cpu);
>> -			continue;
>> +	error = _cpu_up_with_trace(cpu);
>> +	if (cpumask_empty(frozen_cpus))
>> +		goto out;
>> +
>> +	if (error) {
>> +		/*
>> +		 * If fail to bring up the first frozen cpus,
>> +		 * enable the rest frozen cpus on the boot cpu.
>> +		 */
>> +		arch_enable_nonboot_cpus_begin();
>> +		for_each_cpu(cpu, frozen_cpus) {
>> +			_cpu_up_with_trace(cpu);
>>   		}
>> -		pr_warn("Error taking CPU%d up: %d\n", cpu, error);
>> -	}
>> +		arch_enable_nonboot_cpus_end();
>>   
>> -	arch_enable_nonboot_cpus_end();
>> +	} else {
>> +		tsk = kthread_create_on_cpu(async_enable_nonboot_cpus,
>> +				NULL, cpu, "async-enable-nonboot-cpus");

Does it really need to run on the other CPU?  If the idea is to avoid 
waiting mostly, the async thread can start running on the boot CPU just 
fine I suppose.

>> +		if (IS_ERR(tsk)) {
>> +			pr_err("Failed to create async enable nonboot cpus thread.\n");
>> +			goto out;
>> +		}
>>   
>> -	cpumask_clear(frozen_cpus);
>> +		kthread_unpark(tsk);
>> +	}
>>   out:
>>   	cpu_maps_update_done();
>>   }
>>
>

Rafael

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