Commit 9439aab8 authored Jul 19, 2007 by Suresh Siddha Committed by Ingo Molnar Jul 19, 2007

[PATCH] sched: fix newly idle load balance in case of SMT



In the presence of SMT, newly idle balance was never happening for
multi-core and SMP domains (even when both the logical siblings are
idle).

If thread 0 is already idle and when thread 1 is about to go to idle,
newly idle load balance always think that one of the threads is not idle
and skips doing the newly idle load balance for multi-core and SMP
domains.

This is because of the idle_cpu() macro, which checks if the current
process on a cpu is an idle process. But this is not the case for the
thread doing the load_balance_newidle().

Fix this by using runqueue's nr_running field instead of idle_cpu(). And
also skip the logic of 'only one idle cpu in the group will be doing
load balancing' during newly idle case.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent c41917df

kernel/sched.c

+5 −3

Original line number	Diff line number	Diff line
		@@ -2235,7 +2235,7 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,

		rq = cpu_rq(i);

		if (*sd_idle && !idle_cpu(i))
		if (*sd_idle && rq->nr_running)
		*sd_idle = 0;

		/* Bias balancing toward cpus of our domain */
		@@ -2257,9 +2257,11 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
		/*
		* First idle cpu or the first cpu(busiest) in this sched group
		* is eligible for doing load balancing at this and above
		* domains.
		* domains. In the newly idle case, we will allow all the cpu's
		* to do the newly idle load balance.
		*/
		if (local_group && balance_cpu != this_cpu && balance) {
		if (idle != CPU_NEWLY_IDLE && local_group &&
		balance_cpu != this_cpu && balance) {
		*balance = 0;
		goto ret;
		}

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