Messages in this thread Patch in this message | | | Date | Thu, 16 Feb 2006 14:57:24 +1100 | From | Peter Williams <> | Subject | Re: [patch 1/2] fix perf. bug in wake-up load balancing for aim7 and db workload |
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Nick Piggin wrote: > Chen, Kenneth W wrote: > >> Revert commit d7102e95b7b9c00277562c29aad421d2d521c5f6, >> which causes more than 10% performance regression with aim7. >> > > Just to be sure, what kernel did you test with? In particular, > did it have the smpnice patch reverted (as -rc3 does). >
Analysis of the smpnice code indicates that it could cause anomalous cpu selection decisions in try_to_wake_up() if there is a skew in the distribution of nice among the tasks on the cpus under consideration. Attached for review is a proposed patch to address problem. In particular, I request comments on the following issues:
1. Is this potential problem worth worrying about? 2. Do you agree with my decision to replace SCHED_LOAD_SCALE with the average load per task for this_cpu in the if statement in try_to_wake_up() or should I be using the average load per task for the tasks current cpu in one or both places?
Signed-off-by: Peter Williams <pwil3058@bigpond.com.au>
Peter -- 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 2006-02-16 12:39:30.000000000 +1100 +++ MM-2.6.X/kernel/sched.c 2006-02-16 14:36:24.000000000 +1100 @@ -1061,6 +1061,18 @@ static inline unsigned long target_load( } /* + * Return the average load per task on the cpu's run queue + */ +static inline unsigned long cpu_avg_load_per_task(int cpu) +{ + runqueue_t *rq = cpu_rq(cpu); + unsigned long n = rq->nr_running; + unsigned long load = weighted_load(rq->prio_bias); + + return n ? load / n : load; +} + +/* * find_idlest_group finds and returns the least busy CPU group within the * domain. */ @@ -1309,6 +1321,7 @@ static int try_to_wake_up(task_t *p, uns if (this_sd->flags & SD_WAKE_AFFINE) { unsigned long tl = this_load; + unsigned long tl_per_task = cpu_avg_load_per_task(this_cpu); /* * If sync wakeup then subtract the (maximum possible) * effect of the currently running task from the load @@ -1318,8 +1331,8 @@ static int try_to_wake_up(task_t *p, uns tl -= weighted_load(p->bias_prio); if ((tl <= load && - tl + target_load(cpu, idx) <= SCHED_LOAD_SCALE) || - 100*(tl + SCHED_LOAD_SCALE) <= imbalance*load) { + tl + target_load(cpu, idx) <= tl_per_task) || + 100*(tl + tl_per_task) <= imbalance*load) { /* * This domain has SD_WAKE_AFFINE and * p is cache cold in this domain, and | |