From: Steven Rostedt Date: Fri, 17 Jun 2011 01:55:22 +0000 (-0400) Subject: sched: Balance RT tasks when forked as well X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=c37495fd0f64fc139b5a07d242bcb485174d1206;p=openwrt%2Fstaging%2Fblogic.git sched: Balance RT tasks when forked as well When a new task is woken, the code to balance the RT task is currently skipped in the select_task_rq() call. But it will be pushed if the rq is currently overloaded with RT tasks anyway. The issue is that we already queued the task, and if it does get pushed, it will have to be dequeued and requeued on the new run queue. The advantage with pushing it first is that we avoid this requeuing as we are pushing it off before the task is ever queued. See commit 318e0893ce3f524 ("sched: pre-route RT tasks on wakeup") for more details. The return of select_task_rq() when it is not a wake up has also been changed to return task_cpu() instead of smp_processor_id(). This is more of a sanity because the current only other user of select_task_rq() besides wake ups, is an exec, where task_cpu() should also be the same as smp_processor_id(). But if it is used for other purposes, lets keep the task on the same CPU. Why would we mant to migrate it to the current CPU? Signed-off-by: Steven Rostedt Signed-off-by: Peter Zijlstra Cc: Hillf Danton Link: http://lkml.kernel.org/r/20110617015919.832743148@goodmis.org Signed-off-by: Ingo Molnar --- diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c index 70107a39b1ba..2153a87e6157 100644 --- a/kernel/sched_rt.c +++ b/kernel/sched_rt.c @@ -1017,10 +1017,12 @@ select_task_rq_rt(struct task_struct *p, int sd_flag, int flags) struct rq *rq; int cpu; - if (sd_flag != SD_BALANCE_WAKE) - return smp_processor_id(); - cpu = task_cpu(p); + + /* For anything but wake ups, just return the task_cpu */ + if (sd_flag != SD_BALANCE_WAKE && sd_flag != SD_BALANCE_FORK) + goto out; + rq = cpu_rq(cpu); rcu_read_lock(); @@ -1059,6 +1061,7 @@ select_task_rq_rt(struct task_struct *p, int sd_flag, int flags) } rcu_read_unlock(); +out: return cpu; }