Messages in this thread Patch in this message |  | | From | Vaidyanathan Srinivasan <> | | Subject | [RFC PATCH v2 6/7] sched: bias task wakeups to preferred semi-idle packages | | Date | Mon, 08 Sep 2008 18:52:33 +0530 |
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Preferred wakeup cpu (from a semi idle package) has been nominated in find_busiest_group() in the previous patch. Use this information in sched_mc_preferred_wakeup_cpu in function select_task_rq_fair() to bias task wakeups if the following conditions are satisfied: - The present cpu that is trying to wakeup the process is idle and waking the target process on this cpu will potentially wakeup a completely idle package - The previous cpu on which the target process ran is also idle and hence selecting the previous cpu may wakeup a semi idle cpu package - The task being woken up is allowed to run in the nominated cpu (cpu affinity and restrictions)
Basically if both the current cpu and the previous cpu on which the task ran is idle, select the nominated cpu from semi idle cpu package for running the new task that is waking up.
Cache hotness and system utilisation could also be considered before the decision is made. (Not currently implemented)
This technique will effectively move short running bursty jobs in an mostly idle system.
Wakeup biasing for power savings gets automatically disabled if system utilisation increases due to the fact that the probability of finding both this_cpu and prev_cpu idle decreases.
Signed-off-by: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com> ---
kernel/sched_fair.c | 13 +++++++++++++ 1 files changed, 13 insertions(+), 0 deletions(-)
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c index f1c96e3..1301521 100644 --- a/kernel/sched_fair.c +++ b/kernel/sched_fair.c @@ -73,6 +73,9 @@ unsigned int sysctl_sched_wakeup_granularity = 5000000UL; const_debug unsigned int sysctl_sched_migration_cost = 500000UL; +/* Preferred wakeup cpu nominated by sched_mc load balancing logic */ +extern unsigned int sched_mc_preferred_wakeup_cpu; + /************************************************************** * CFS operations on generic schedulable entities: */ @@ -1232,6 +1235,16 @@ static int select_task_rq_fair(struct task_struct *p, int sync) } } + /* + * At POWERSAVINGS_BALANCE_WAKEUP level, if both this_cpu and prev_cpu + * are idle and this is not a kernel thread and this task's affinity + * allows it to be moved to preferred cpu, then just move! + */ + if (sched_mc_power_savings >= POWERSAVINGS_BALANCE_WAKEUP && + idle_cpu(prev_cpu) && idle_cpu(this_cpu) && p->mm && + cpu_isset(sched_mc_preferred_wakeup_cpu, p->cpus_allowed)) + return sched_mc_preferred_wakeup_cpu; + if (unlikely(!cpu_isset(this_cpu, p->cpus_allowed))) goto out;
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