Re: [PATCH 1/2] x86/cpu hotplug: make apicid <--> cpuid mapping persistent

[Gu Zheng <guz.fnst@cn.fujitsu.com>]

Hi Kame-san,

On 03/27/2015 12:31 AM, Kamezawa Hiroyuki wrote:

> On 2015/03/26 13:55, Gu Zheng wrote:
>> Hi Kame-san,
>> On 03/26/2015 11:19 AM, Kamezawa Hiroyuki wrote:
>>
>>> On 2015/03/26 11:17, Gu Zheng wrote:
>>>> Previously, we build the apicid <--> cpuid mapping when the cpu is present, but
>>>> the relationship will be changed if the cpu/node hotplug happenned, because we
>>>> always choose the first free cpuid for the hot added cpu (whether it is new-add
>>>> or re-add), so this the cpuid <--> node mapping changed if node hot plug
>>>> occurred, and it causes the wq sub-system allocation failture:
>>>>     ==
>>>>        SLUB: Unable to allocate memory on node 2 (gfp=0x80d0)
>>>>         cache: kmalloc-192, object size: 192, buffer size: 192, default
>>>> order:
>>>>       1, min order: 0
>>>>         node 0: slabs: 6172, objs: 259224, free: 245741
>>>>         node 1: slabs: 3261, objs: 136962, free: 127656
>>>>     ==
>>>> So here we build the persistent [lapic id] <--> cpuid mapping when the cpu first
>>>> present, and never change it.
>>>>
>>>> Suggested-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>>>> Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
>>>> ---
>>>>    arch/x86/kernel/apic/apic.c |   31 ++++++++++++++++++++++++++++++-
>>>>    1 files changed, 30 insertions(+), 1 deletions(-)
>>>>
>>>> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
>>>> index ad3639a..d539ebc 100644
>>>> --- a/arch/x86/kernel/apic/apic.c
>>>> +++ b/arch/x86/kernel/apic/apic.c
>>>> @@ -2038,6 +2038,30 @@ void disconnect_bsp_APIC(int virt_wire_setup)
>>>>    	apic_write(APIC_LVT1, value);
>>>>    }
>>>>    
>>>> +/*
>>>> + * Logic cpu number(cpuid) to local APIC id persistent mappings.
>>>> + * Do not clear the mapping even if cpu hot removed.
>>>> + * */
>>>> +static int apicid_to_x86_cpu[MAX_LOCAL_APIC] = {
>>>> +	[0 ... MAX_LOCAL_APIC - 1] = -1,
>>>> +};
>>>
>>>
>>> This patch cannot handle x2apic, which is 32bit.
>>
>> IMO, if the apicid is too big (larger than MAX_LOCAL_APIC), we will skip
>> generating a logic cpu number for it, so it seems no problem here.
>>
> you mean MAX_LOCAL_APIC=32768 ? ....isn't it too wasting ?

I use the big array here to keep the same format with the existed ones:
int apic_version[MAX_LOCAL_APIC];

s16 __apicid_to_node[MAX_LOCAL_APIC] = {
	[0 ... MAX_LOCAL_APIC-1] = NUMA_NO_NODE
};
Or we should also say "NO" to them?

Regards,
Gu

> 
> Anyway, APIC IDs are sparse values. Please use proper structure.
> 
> Thanks,
> -Kame
> 
>>>
>>> As far as I understand, it depends on CPU's spec and the newest cpu has 9bit apicid, at least.
>>>
>>> But you can't create inifinit array.
>>>
>>> If you can't allocate the array dynamically, How about adding
>>>
>>>   static int cpuid_to_apicid[MAX_CPU] = {}
>>>
>>> or using idr library ? (please see lib/idr.c)
>>>
>>> I guess you can update this map after boot(after mm initialization)
>>> and make use of idr library.
>>>
>>> About this patch, Nack.
>>>
>>> -Kame
>>>
>>>
>>>
>>>> +
>>>> +/*
>>>> + * Internal cpu id bits, set the bit once cpu present, and never clear it.
>>>> + * */
>>>> +static cpumask_t cpuid_mask = CPU_MASK_NONE;
>>>> +
>>>> +static int get_cpuid(int apicid)
>>>> +{
>>>> +	int cpuid;
>>>> +
>>>> +	cpuid = apicid_to_x86_cpu[apicid];
>>>> +	if (cpuid == -1)
>>>> +		cpuid = cpumask_next_zero(-1, &cpuid_mask);
>>>> +
>>>> +	return cpuid;
>>>> +}
>>>> +
>>>>    int generic_processor_info(int apicid, int version)
>>>>    {
>>>>    	int cpu, max = nr_cpu_ids;
>>>> @@ -2115,7 +2139,10 @@ int generic_processor_info(int apicid, int version)
>>>>    		 */
>>>>    		cpu = 0;
>>>>    	} else
>>>> -		cpu = cpumask_next_zero(-1, cpu_present_mask);
>>>> +		cpu = get_cpuid(apicid);
>>>> +
>>>> +	/* Store the mapping */
>>>> +	apicid_to_x86_cpu[apicid] = cpu;
>>>>    
>>>>    	/*
>>>>    	 * Validate version
>>>> @@ -2144,6 +2171,8 @@ int generic_processor_info(int apicid, int version)
>>>>    	early_per_cpu(x86_cpu_to_logical_apicid, cpu) =
>>>>    		apic->x86_32_early_logical_apicid(cpu);
>>>>    #endif
>>>> +	/* Mark this cpu id as uesed (already mapping a local apic id) */
>>>> +	cpumask_set_cpu(cpu, &cpuid_mask);
>>>>    	set_cpu_possible(cpu, true);
>>>>    	set_cpu_present(cpu, true);
>>>>    
>>>>
>>>
>>>
>>> .
>>>
>>
>>
> 
> 
> .
>