Messages in this thread | | | Date | Mon, 22 Jun 2015 18:28:55 -0400 | From | Rik van Riel <> | Subject | Re: [PATCH] sched,numa: document and fix numa_preferred_nid setting |
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On 06/22/2015 12:13 PM, Srikar Dronamraju wrote: >> + * migrating the task to where it really belongs. >> + * The exception is a task that belongs to a large numa_group, which >> + * spans multiple NUMA nodes. If that task migrates into one of the >> + * workload's active nodes, remember that node as the task's >> + * numa_preferred_nid, so the workload can settle down. >> */ >> if (p->numa_group) { >> if (env.best_cpu == -1) >> @@ -1513,7 +1520,7 @@ static int task_numa_migrate(struct task_struct *p) >> nid = env.dst_nid; >> >> if (node_isset(nid, p->numa_group->active_nodes)) >> - sched_setnuma(p, env.dst_nid); >> + sched_setnuma(p, nid); >> } >> >> /* No better CPU than the current one was found. */ >> > > When I refer to the Modified Rik's patch, I mean to remove the > node_isset() check before the sched_setnuma. With that change, we kind > of reduce the numa02 and 1JVMper System regression while getting as good > numbers as Rik's patch with 2JVM and 4JVM per System. > > The idea behind removing the node_isset check is: > node_isset is mostly used to track mem movement to nodes where cpus are > running and not vice versa. This is as per comment in > update_numa_active_node_mask. There could be a sitation where task memory > is all in a node and the node has capacity to accomodate but no tasks > associated with the task have run enuf on that node. In such a case, we > shouldnt be ruling out migrating the task to the node.
That is a good point.
However, if overriding the preferred_nid that task_numa_placement identified is a good idea in task_numa_migrate, would it also be a good idea for tasks that are NOT part of a numa group?
What are the consequences of never setting preferred_nid from task_numa_migrate? (we would try to migrate the task to a better node more frequently)
What are the consequences of always setting preferred_nid from task_numa_migrate? (we would only try migrating the task once, and it could get stuck in a sub-optimal location)
The patch seems to work, but I do not understand why, and would like to know your ideas on why you think the patch works.
I am really not looking forward to the idea of maintaining code that nobody understands...
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