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authorVaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>2008-12-18 12:56:36 -0500
committerIngo Molnar <mingo@elte.hu>2008-12-19 03:21:54 -0500
commitad273b32e482cdef306eac32b28d97f513a022f4 (patch)
tree230ba0c2f8b594f4acefe5f5b219c650b7b0cb07
parent7eb52dfa70dbf5232b5b83ec4357e6bebaa8fde8 (diff)
sched: activate active load balancing in new idle cpus
Impact: tweak task balancing to save power more agressively Active load balancing is a process by which migration thread is woken up on the target CPU in order to pull current running task on another package into this newly idle package. This method is already in use with normal load_balance(), this patch introduces this method to new idle cpus when sched_mc is set to POWERSAVINGS_BALANCE_WAKEUP. This logic provides effective consolidation of short running daemon jobs in a almost idle system The side effect of this patch may be ping-ponging of tasks if the system is moderately utilised. May need to adjust the iterations before triggering. Signed-off-by: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com> Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Ingo Molnar <mingo@elte.hu>
-rw-r--r--kernel/sched.c54
1 files changed, 54 insertions, 0 deletions
diff --git a/kernel/sched.c b/kernel/sched.c
index c1b8b3031eb2..8fc0d5aa43b1 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3670,10 +3670,64 @@ redo:
3670 } 3670 }
3671 3671
3672 if (!ld_moved) { 3672 if (!ld_moved) {
3673 int active_balance;
3674
3673 schedstat_inc(sd, lb_failed[CPU_NEWLY_IDLE]); 3675 schedstat_inc(sd, lb_failed[CPU_NEWLY_IDLE]);
3674 if (!sd_idle && sd->flags & SD_SHARE_CPUPOWER && 3676 if (!sd_idle && sd->flags & SD_SHARE_CPUPOWER &&
3675 !test_sd_parent(sd, SD_POWERSAVINGS_BALANCE)) 3677 !test_sd_parent(sd, SD_POWERSAVINGS_BALANCE))
3676 return -1; 3678 return -1;
3679
3680 if (sched_mc_power_savings < POWERSAVINGS_BALANCE_WAKEUP)
3681 return -1;
3682
3683 if (sd->nr_balance_failed++ < 2)
3684 return -1;
3685
3686 /*
3687 * The only task running in a non-idle cpu can be moved to this
3688 * cpu in an attempt to completely freeup the other CPU
3689 * package. The same method used to move task in load_balance()
3690 * have been extended for load_balance_newidle() to speedup
3691 * consolidation at sched_mc=POWERSAVINGS_BALANCE_WAKEUP (2)
3692 *
3693 * The package power saving logic comes from
3694 * find_busiest_group(). If there are no imbalance, then
3695 * f_b_g() will return NULL. However when sched_mc={1,2} then
3696 * f_b_g() will select a group from which a running task may be
3697 * pulled to this cpu in order to make the other package idle.
3698 * If there is no opportunity to make a package idle and if
3699 * there are no imbalance, then f_b_g() will return NULL and no
3700 * action will be taken in load_balance_newidle().
3701 *
3702 * Under normal task pull operation due to imbalance, there
3703 * will be more than one task in the source run queue and
3704 * move_tasks() will succeed. ld_moved will be true and this
3705 * active balance code will not be triggered.
3706 */
3707
3708 /* Lock busiest in correct order while this_rq is held */
3709 double_lock_balance(this_rq, busiest);
3710
3711 /*
3712 * don't kick the migration_thread, if the curr
3713 * task on busiest cpu can't be moved to this_cpu
3714 */
3715 if (!cpu_isset(this_cpu, busiest->curr->cpus_allowed)) {
3716 double_unlock_balance(this_rq, busiest);
3717 all_pinned = 1;
3718 return ld_moved;
3719 }
3720
3721 if (!busiest->active_balance) {
3722 busiest->active_balance = 1;
3723 busiest->push_cpu = this_cpu;
3724 active_balance = 1;
3725 }
3726
3727 double_unlock_balance(this_rq, busiest);
3728 if (active_balance)
3729 wake_up_process(busiest->migration_thread);
3730
3677 } else 3731 } else
3678 sd->nr_balance_failed = 0; 3732 sd->nr_balance_failed = 0;
3679 3733