Re: [LTP] NUMA system and get_a_numa_node()

[Wanlong Gao <gaowanlong@cn.fujitsu.com>]

On 11/27/2014 03:45 PM, Han Pingtian wrote:
> On Thu, Nov 27, 2014 at 11:06:15AM +0800, Wanlong Gao wrote:
>> On 11/27/2014 10:42 AM, Han Pingtian wrote:
>>> On Wed, Nov 26, 2014 at 01:53:36PM +0100, Cyril Hrubis wrote:
>>>> Hi!
>>>>> We have a system which only has one NUMA node. When trying to run ksm02
>>>>> on it, becase the code calling get_allowed_nodes() with a count 2 as
>>>>> below:
>>>>>
>>>>>  972 /* Warning: *DO NOT* use this function in child */
>>>>>  973 unsigned int get_a_numa_node(void (*cleanup_fn) (void))
>>>>>  974 {              
>>>>>  975         unsigned int nd1, nd2;
>>>>>  976         int ret; 
>>>>>  977                        
>>>>>  978         ret = get_allowed_nodes(0, 2, &nd1, &nd2);
>>>>>  979         switch (ret) { 
>>>>>  980         case 0:
>>>>>  981                 break;
>>>>>  982         case -3:
>>>>>  983                 tst_brkm(TCONF, cleanup_fn, "requires a NUMA system.");
>>>>>
>>>>> it always failed with "requires a NUMA system.".
>>>>>
>>>>> I think a NUMA system may have only one node, right? If so, could we
>>>>> change the count to 1?
>>>>
>>>> Hmm, are you sure that the testcases are actually applicable to a system
>>>> with only one node?
>>>>
>>>> Because what the testcases do in the setup is to write 1 to
>>>> /sys/kernel/mm/ksm/merge_across_nodes so I would expect that the test
>>>> needs at least two nodes...
>>>>
>>> I think if there is only one NUMA node, then this is a special case for
>>> this testcase, it'll test if set "merge_across_nodes" to 1, any problem
>>> will be triggered.
>>>
>>> I have tried to change the node count to 1 in get_allowed_nodes() and
>>> recompiled ksm02. It works successfully.
>>>
>>
>>
>> Do you think ONLY ONE NODE can be called NUMA?
>>
>> http://en.wikipedia.org/wiki/Non-uniform_memory_access
>>
> 
> I think it's not a problem to run the testcase on a non-NUMA system, if
> we take it as a special case?

It's meaningless, the "special case" you said is already there, it's ksm01.

Thanks,
Wanlong Gao

> 
> Thanks.
> 
> 
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