lkml.org 
[lkml]   [2014]   [May]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 2/4] sched,numa: weigh nearby nodes for task placement on complex NUMA topologies
On 05/09/2014 06:11 AM, Peter Zijlstra wrote:
> On Thu, May 08, 2014 at 01:23:29PM -0400, riel@redhat.com wrote:
>> @@ -930,7 +987,7 @@ static inline unsigned long group_faults_cpu(struct numa_group *group, int nid)
>> */
>> static inline unsigned long task_weight(struct task_struct *p, int nid)
>> {
>> - unsigned long total_faults;
>> + unsigned long total_faults, score;
>>
>> if (!p->numa_faults_memory)
>> return 0;
>> @@ -940,15 +997,32 @@ static inline unsigned long task_weight(struct task_struct *p, int nid)
>> if (!total_faults)
>> return 0;
>>
>> - return 1000 * task_faults(p, nid) / total_faults;
>> + score = 1000 * task_faults(p, nid);
>> + score += nearby_nodes_score(p, nid, true);
>> +
>> + score /= total_faults;
>> +
>> + return score;
>> }
>>
>> static inline unsigned long group_weight(struct task_struct *p, int nid)
>> {
>> - if (!p->numa_group || !p->numa_group->total_faults)
>> + unsigned long total_faults, score;
>> +
>> + if (!p->numa_group)
>> + return 0;
>> +
>> + total_faults = p->numa_group->total_faults;
>> +
>> + if (!total_faults)
>> return 0;
>>
>> - return 1000 * group_faults(p, nid) / p->numa_group->total_faults;
>> + score = 1000 * group_faults(p, nid);
>> + score += nearby_nodes_score(p, nid, false);
>> +
>> + score /= total_faults;
>> +
>> + return score;
>> }
>
> OK, and that's just sad..
>
> See task_numa_placement(), which does:
>
> for_each_online_node(nid) {
> weight = task_weight(p, nid) + group_weight(p, nid);
> if (weight > max_weight) {
> max_weight = weight;
> max_nid = nid;
> }
> }
>
> So not only is that loop now O(nr_nodes^2), the inner loops doubly
> iterates all nodes.

I am not too worried about task_numa_placement, but you are
right that this may well be much too expensive for more
frequently called code like migrate_improves_locality.

Having said that, grouping related tasks together on nearby
nodes does seem to bring significant performance gains.

Do you have any ideas on other ways we can achieve that
grouping?

> Also, {task,group}_weight() functions were like cheap-ish (/me mumbles
> something about people using !2^n scaling factors for no sane reason).
> And they're used all over with that in mind.
>
> But look what you did to migrate_improves_locality(), that will now
> iterate all nodes _4_ times, and its called for every single task we try
> and migrate during load balance, while holding rq->lock.
>
>



\
 
 \ /
  Last update: 2014-05-09 18:01    [W:0.169 / U:0.028 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site