From 1bd77f2da58e9cdd1f159217887343dadd9af417 Mon Sep 17 00:00:00 2001 From: Christoph Lameter Date: Sun, 10 Dec 2006 02:20:27 -0800 Subject: [PATCH] [PATCH] sched: call tasklet less frequently Trigger softirq less frequently We trigger the softirq before this patch using offset of sd->interval. However, if the queue is busy then it is sufficient to schedule the softirq with sd->interval * busy_factor. So we modify the calculation of the next time to balance by taking the interval added to last_balance again. This is only the right value if the idle/busy situation continues as is. There are two potential trouble spots: - If the queue was idle and now gets busy then we call rebalance early. However, that is not a problem because we will then use the longer interval for the next period. - If the queue was busy and becomes idle then we potentially wait too long before rebalancing. However, when the task goes idle then idle_balance is called. We add another calculation of the next balance time based on sd->interval in idle_balance so that we will rebalance soon. V2->V3: - Calculate rebalance time based on current jiffies and not based on the jiffies at the last time we load balanced. We no longer rely on staggering and therefore we can affort to do this now. V3->V4: - Use functions to do jiffy comparisons. Signed-off-by: Christoph Lameter Cc: Peter Williams Cc: Nick Piggin Cc: Christoph Lameter Cc: "Siddha, Suresh B" Cc: "Chen, Kenneth W" Acked-by: Ingo Molnar Cc: KAMEZAWA Hiroyuki Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/sched.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) diff --git a/kernel/sched.c b/kernel/sched.c index 0a3e748d73..0a4a26b21f 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -2774,14 +2774,28 @@ out_balanced: static void idle_balance(int this_cpu, struct rq *this_rq) { struct sched_domain *sd; + int pulled_task = 0; + unsigned long next_balance = jiffies + 60 * HZ; for_each_domain(this_cpu, sd) { if (sd->flags & SD_BALANCE_NEWIDLE) { /* If we've pulled tasks over stop searching: */ - if (load_balance_newidle(this_cpu, this_rq, sd)) + pulled_task = load_balance_newidle(this_cpu, + this_rq, sd); + if (time_after(next_balance, + sd->last_balance + sd->balance_interval)) + next_balance = sd->last_balance + + sd->balance_interval; + if (pulled_task) break; } } + if (!pulled_task) + /* + * We are going idle. next_balance may be set based on + * a busy processor. So reset next_balance. + */ + this_rq->next_balance = next_balance; } /* @@ -2904,7 +2918,7 @@ static void run_rebalance_domains(struct softirq_action *h) */ idle = NOT_IDLE; } - sd->last_balance += interval; + sd->last_balance = jiffies; } if (time_after(next_balance, sd->last_balance + interval)) next_balance = sd->last_balance + interval; -- 2.39.5