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

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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>
This commit is contained in:
Suresh Siddha 2007-07-19 21:28:35 +02:00 • committed by Ingo Molnar
parent c41917df8a
commit 9439aab8db
1 changed files with 5 additions and 3 deletions
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8
kernel/sched.c
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@ -2235,7 +2235,7 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
rq = cpu_rq(i); rq = cpu_rq(i);
if (*sd_idle && !idle_cpu(i)) if (*sd_idle && rq->nr_running)
*sd_idle = 0; *sd_idle = 0;
/* Bias balancing toward cpus of our domain */ /* 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 * First idle cpu or the first cpu(busiest) in this sched group
* is eligible for doing load balancing at this and above * 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; *balance = 0;
goto ret; goto ret;
} }