Messages in this thread Patch in this message | | | Date | Tue, 04 Apr 2006 16:19:17 +1000 | From | Peter Williams <> | Subject | [PATCH] sched: improve smpnice load balancing when load per task imbalanced |
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Problem:
2 CPU system: if the cpu-0 has two high priority and cpu-1 has one normal priority task, how can the current code detect this imbalance because imbalance will be always < busiest_load_per_task and max_load - this_load will be < 2 * busiest_load_per_task and pwr_move will be <= pwr_now.
Solution:
Modify the assessment of small imbalances to take into account the relative sizes of busiest_load_per_task and this_load_per_task. This is exploiting the fact that if the difference between the loads is greater than busiest_load_per_task and busiest_load_per_task is greater than this_load_per_task then moving busiest_load_per_task worth of load from busiest to this will be an improvement in the distribution of weighted load.
Required patches:
sched-prevent-high-load-weight-tasks-suppressing-balancing.patch sched-improve-stability-of-smpnice-load-balancing.patch
Note: This patch makes no change to load balancing in the case where all tasks are nice==0.
Signed-off-by: Peter Williams <pwil3058@bigpond.com.au>
-- Peter Williams pwil3058@bigpond.net.au
"Learning, n. The kind of ignorance distinguishing the studious." -- Ambrose Bierce
Index: MM-2.6.X/kernel/sched.c =================================================================== --- MM-2.6.X.orig/kernel/sched.c 2006-04-04 15:18:19.000000000 +1000 +++ MM-2.6.X/kernel/sched.c 2006-04-04 15:53:48.000000000 +1000 @@ -2252,8 +2252,16 @@ find_busiest_group(struct sched_domain * if (*imbalance < busiest_load_per_task) { unsigned long pwr_now = 0, pwr_move = 0; unsigned long tmp; + unsigned int imbn = 2; - if (max_load - this_load >= busiest_load_per_task*2) { + if (this_nr_running) { + this_load_per_task /= this_nr_running; + if (busiest_load_per_task > this_load_per_task) + imbn = 1; + } else + this_load_per_task = SCHED_LOAD_SCALE; + + if (max_load - this_load >= busiest_load_per_task * imbn) { *imbalance = busiest_load_per_task; return busiest; } @@ -2266,10 +2274,6 @@ find_busiest_group(struct sched_domain * pwr_now += busiest->cpu_power * min(busiest_load_per_task, max_load); - if (this_nr_running) - this_load_per_task /= this_nr_running; - else - this_load_per_task = SCHED_LOAD_SCALE; pwr_now += this->cpu_power * min(this_load_per_task, this_load); pwr_now /= SCHED_LOAD_SCALE; | |