linux-kernel - Re: [PATCH v10 2/7] x86, acpi, cpu-hotplug: Enable acpi to register all possible cpus at boot time.

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Date:	Tue, 2 Aug 2016 15:30:38 +0800
From:	Dou Liyang <douly.fnst@...fujitsu.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	<cl@...ux.com>, <tj@...nel.org>, <mika.j.penttila@...il.com>,
	<mingo@...hat.com>, <akpm@...ux-foundation.org>,
	<rjw@...ysocki.net>, <hpa@...or.com>, <yasu.isimatu@...il.com>,
	<isimatu.yasuaki@...fujitsu.com>, <kamezawa.hiroyu@...fujitsu.com>,
	<izumi.taku@...fujitsu.com>, <gongzhaogang@...pur.com>,
	<len.brown@...el.com>, <lenb@...nel.org>, <chen.tang@...ystack.cn>,
	<rafael@...nel.org>, <x86@...nel.org>,
	<linux-acpi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-mm@...ck.org>, Gu Zheng <guz.fnst@...fujitsu.com>,
	Tang Chen <tangchen@...fujitsu.com>,
	Zhu Guihua <zhugh.fnst@...fujitsu.com>
Subject: Re: [PATCH v10 2/7] x86, acpi, cpu-hotplug: Enable acpi to register
 all possible cpus at boot time.

Hi tglx,

在 2016年07月29日 21:36, Thomas Gleixner 写道:
> On Tue, 26 Jul 2016, Dou Liyang wrote:
>
>> 1. Enable apic registeration flow to handle both enabled and disabled cpus.
>>    This is done by introducing an extra parameter to generic_processor_info to
>>    let the caller control if disabled cpus are ignored.
>
> If I'm reading the patch correctly then the 'enabled' argument controls more
> than the disabled cpus accounting. It also controls the modification of
> num_processors and the present mask.

In the patch, they both need mapping to a logic cpu.
As you said, the 'enabled' controls extra functions:

1. num_processors parameter
2. physid_set method
3. set_cpu_present method

>
>> -int generic_processor_info(int apicid, int version)
>> +static int __generic_processor_info(int apicid, int version, bool enabled)
>>  {
>>  	int cpu, max = nr_cpu_ids;
>>  	bool boot_cpu_detected = physid_isset(boot_cpu_physical_apicid,
>> @@ -2032,7 +2032,8 @@ int generic_processor_info(int apicid, int version)
>>  			   " Processor %d/0x%x ignored.\n",
>>  			   thiscpu, apicid);
>>
>> -		disabled_cpus++;
>> +		if (enabled)
>> +			disabled_cpus++;
>>  		return -ENODEV;
>>  	}
>>
>> @@ -2049,7 +2050,8 @@ int generic_processor_info(int apicid, int version)
>>  			" reached. Keeping one slot for boot cpu."
>>  			"  Processor %d/0x%x ignored.\n", max, thiscpu, apicid);
>>
>> -		disabled_cpus++;
>> +		if (enabled)
>> +			disabled_cpus++;
>
> This is utterly confusing. That code path cannot be reached when enabled is
> false, because num_processors is 0 as we never increment it when enabled is
> false.
>
> That said, I really do not like this 'slap some argument on it and make it
> work somehow' approach.
>
> The proper solution for this is to seperate out the functionality which you
> need for the preparation run (enabled = false) and make sure that the
> information you need for the real run (enabled = true) is properly cached
> somewhere so we don't have to evaluate the same thing over and over.

Thank you very much for your advice. That solution is very good for me.

I thought about the differences between them carefully. Firstly, I
intend to separate out the functionality in two functions. It's simple
but not good. Then, I try to put them together to judge just once.

After, considering the judgment statement independence and the order of
assignment. I remove all the "if (enabled)" code and do the unified
judgment like this:

@@ -2180,12 +2176,19 @@ int __generic_processor_info(int apicid, int
version, bool enabled)
                 apic->x86_32_early_logical_apicid(cpu);
  #endif
         set_cpu_possible(cpu, true);
-       if (enabled)
+
+       if (enabled){
+               num_processors++;
+               physid_set(apicid, phys_cpu_present_map);
                 set_cpu_present(cpu, true);
+       }else{
+               disabled_cpus++;
+       }

         return cpu;
  }

I hope that patch could consistent with your advice. And I will submit
the detailed modification in the next version patches.

Thanks,

Dou.