sched: Fix group_capacity for sched_smt_powersavings=1
PATCH 1/1 sched: Fix group_capacity for sched_smt_powersavings=1
Hi Peter,
This is repost of the same patch http://lkml.org/lkml/2010/3/22/275
(and http://lkml.org/lkml/2010/3/2/216)
After applying Suresh's fixes from discussion thread
http://lkml.org/lkml/2010/2/12/352, we still need the attached patch to restore sched_smt_powersavings=1 functionality where tasks prefer sibling threads and keep more cores idle.
Please apply to sched-tip, the patch is rebased and tested on today's sched-tip master.
The attached patch will run 4 while(1) loops in two cores when sched_smt_power_savings=1. Tested on two socket, quad core, hyper threaded system.
Additional testing was done on POWER platform where sched_smt_powersavings was able to consolidate tasks on sibling threads leaving more idle cores.
Thanks,
Vaidy
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sched: Fix group_capacity for sched_smt_powersavings=1
sched_smt_powersavings for threaded systems need this fix for consolidation to sibling threads to work. Since threads have fractional capacity, group_capacity will turn out to be one always and not accommodate another task in the sibling thread.
This fix makes group_capacity a function of cpumask_weight that will enable the power saving load balancer to pack tasks among sibling threads and keep more cores idle.
kernel/sched_fair.c +17 -1
@@ -2538,6 +2538,21 @@ static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu,*/ if (prefer_sibling) sgs.group_capacity =min (sgs.group_capacity,1UL ); +/* +* If power savings balance is set at this domain, then +* make capacity equal to number of hardware threads to +* accommodate more tasks until capacity is reached. +*/ +else if (sd->flags &SD_POWERSAVINGS_BALANCE ) + sgs.group_capacity = +cpumask_weight (sched_group_cpus (group)); + +/* +* The default group_capacity is rounded from sum of +* fractional cpu_powers of sibling hardware threads +* in order to enable fair use of available hardware +* resources. +*/ if (local_group) { sds->this_load = sgs.avg_load;
@@ -2863,7 +2878,8 @@ static int need_active_balance(struct sched_domain *sd, int sd_idle, int idle) !test_sd_parent(sd, SD_POWERSAVINGS_BALANCE))return 0 ; -if (sched_mc_power_savings <POWERSAVINGS_BALANCE_WAKEUP ) +if (sched_mc_power_savings <POWERSAVINGS_BALANCE_WAKEUP && + sched_smt_power_savings <POWERSAVINGS_BALANCE_WAKEUP )return 0 ; }