Messages in this thread | | | From | Vincent Guittot <> | Date | Thu, 13 Feb 2020 17:38:31 +0100 | Subject | Re: [RFC 2/4] sched/numa: replace runnable_load_avg by load_avg |
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On Thu, 13 Feb 2020 at 17:34, Mel Gorman <mgorman@techsingularity.net> wrote: > > On Thu, Feb 13, 2020 at 05:11:23PM +0100, Vincent Guittot wrote: > > > On Thu, Feb 13, 2020 at 10:00:26AM -0500, Phil Auld wrote: > > > > On Thu, Feb 13, 2020 at 01:46:55PM +0000 Mel Gorman wrote: > > > > > On Thu, Feb 13, 2020 at 09:16:58PM +0800, Hillf Danton wrote: > > > > > > > - load = task_h_load(env->p); > > > > > > > - dst_load = env->dst_stats.load + load; > > > > > > > - src_load = env->src_stats.load - load; > > > > > > > - > > > > > > > /* > > > > > > > - * If the improvement from just moving env->p direction is better > > > > > > > - * than swapping tasks around, check if a move is possible. > > > > > > > + * If dst node has spare capacity, then check if there is an > > > > > > > + * imbalance that would be overruled by the load balancer. > > > > > > > */ > > > > > > > - maymove = !load_too_imbalanced(src_load, dst_load, env); > > > > > > > + if (env->dst_stats.node_type == node_has_spare) { > > > > > > > + unsigned int imbalance; > > > > > > > + int src_running, dst_running; > > > > > > > + > > > > > > > + /* Would movement cause an imbalance? */ > > > > > > > + src_running = env->src_stats.nr_running - 1; > > > > > > > + dst_running = env->src_stats.nr_running + 1; > > > > > > > + imbalance = max(0, dst_running - src_running); > > > > > > > > > > > > Have trouble working out why 2 is magician again to make your test data nicer :P > > > > > > > > > > > > > > > > This is calculating what the nr_running would be after the move and > > > > > checking if an imbalance exists after the move forcing the load balancer > > > > > to intervene. > > > > > > > > Isn't that always going to work out to 2? > > > > > > > > > > Crap, stupid cut and paste moving between source trees. Yes, this is > > > broken. > > > > On the load balance side we have 2 rules when NUMA groups has spare capacity: > > - ensure that the diff between src and dst nr_running < 2 > > - if src_nr_running is lower than 2, allow a degree of imbalance of 2 > > instead of 1 > > > > Your test doesn't explicitly ensure that the 1 condition is met > > > > That being said, I'm not sure it's really a wrong thing ? I mean > > load_balance will probably try to pull back some tasks on src but as > > long as it is not a task with dst node as preferred node, it should > > not be that harmfull > > My thinking was that if source has as many or more running tasks than > the destination *after* the move that it's not harmful and does not add > work for the load balancer.
load_balancer will see an imbalance but fbq_classify_group/queue should be there to prevent from pulling back tasks that are on the preferred node but only other tasks
> > -- > Mel Gorman > SUSE Labs
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