linux-kernel - Re: [PATCH x86/mm UPDATED] x86-64, NUMA: Fix distance table handling

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Date:	Wed, 02 Mar 2011 10:52:28 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Tejun Heo <tj@...nel.org>
CC:	David Rientjes <rientjes@...gle.com>, Ingo Molnar <mingo@...e.hu>,
	tglx@...utronix.de, "H. Peter Anvin" <hpa@...or.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH x86/mm UPDATED] x86-64, NUMA: Fix distance table handling

On 03/02/2011 08:55 AM, Tejun Heo wrote:
> On Wed, Mar 02, 2011 at 08:46:17AM -0800, Yinghai Lu wrote:
>>> * I don't think it's gonna matter all that much.  It's one time and
>>>   only used if emulation is enabled, but then again yeap MAX_NUMNODES
>>>   * MAX_NUMNODES can get quite high, but it looks way too complicated
>>>   for what it achieves.  Just looping over enabled nodes should
>>>   achieve about the same thing in much simpler way, right?
>>
>> what kind of excuse to put inefficiency code there!
> 
> Complexity of a solution should match the benefit of the complexity.
> Code complexity is one of the most important metrics that we need to
> keep an eye on.  If you don't do that, the code base becomes very ugly
> and difficult to maintain very quickly.  So, yes, some amount of
> execution inefficiency is acceptable depending on circumstances.
> Efficiency too is something which should be traded off against other
> benefits.

No. it is not acceptable in your case.

We can accept that something like: during init stage, do some probe and call pathes to be happy.
like subarch.

Also why did you omit my first question?

>>>>diff --git a/arch/x86/mm/numa_64.c b/arch/x86/mm/numa_64.c
>>>>> index 7757d22..541746f 100644
>>>>> --- a/arch/x86/mm/numa_64.c
>>>>> +++ b/arch/x86/mm/numa_64.c
>>>>> @@ -390,14 +390,12 @@ static void __init numa_nodemask_from_meminfo(nodemask_t *nodemask,
>>>>>   */
>>>>>  void __init numa_reset_distance(void)
>>>>>  {
>>>>> -	size_t size;
>>>>> +	size_t size = numa_distance_cnt * numa_distance_cnt * sizeof(numa_distance[0]);
>>>>>  
>>>>> -	if (numa_distance_cnt) {
>>>>> -		size = numa_distance_cnt * sizeof(numa_distance[0]);
>>>>> +	if (numa_distance_cnt)
>>>>>  		memblock_x86_free_range(__pa(numa_distance),
>>>>>  					__pa(numa_distance) + size);
>>>>> -		numa_distance_cnt = 0;
>>>>> -	}
>>>>> +	numa_distance_cnt = 0;
>>>>>  	numa_distance = NULL;
>>>>>  }

>> my original part:
>> >>
>> >> @@ -393,7 +393,7 @@ void __init numa_reset_distance(void)
>> >>         size_t size;
>> >>  
>> >>         if (numa_distance_cnt) {
>> >> -               size = numa_distance_cnt * sizeof(numa_distance[0]);
>> >> +               size = numa_distance_cnt * numa_distance_cnt * sizeof(numa_distance[0]);
>> >>                 memblock_x86_free_range(__pa(numa_distance),
>> >>                                         __pa(numa_distance) + size);
>> >>                 numa_distance_cnt = 0;
>> >>
>> >> So can you tell me why you need to make those change?
>> >> 	move out assigning or numa_distance_cnt and size of the the IF
> > 
> > Please read the patch description.  I actually wrote that down.  :-)
well you said:
> > while at it, take numa_distance_cnt resetting in
> > numa_reset_distance() out of the if block to simplify the code a bit.
what are you talking about? what do you mean "simplify the code a bit" ?

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