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authorPaul Turner <pjt@google.com>2011-01-21 20:45:03 -0800
committerIngo Molnar <mingo@elte.hu>2011-01-26 12:33:19 +0100
commitf07333bf6ee66d9b49286cec4371cf375e745b7a (patch)
tree03a1e9968eadf2465b6fc04fb8c1ab67327ea0f2
parent6d5ab2932a21ea54406ab95c43ecff90a3eddfda (diff)
sched: Avoid expensive initial update_cfs_load()
Since cfs->{load_stamp,load_last} are zero-initalized the initial load update will consider the delta to be 'since the beginning of time'. This results in a lot of pointless divisions to bring this large period to be within the sysctl_sched_shares_window. Fix this by initializing load_stamp to be 1 at cfs_rq initialization, this allows for an initial load_stamp > load_last which then lets standard idle truncation proceed. We avoid spinning (and slightly improve consistency) by fixing delta to be [period - 1] in this path resulting in a slightly more predictable shares ramp. (Previously the amount of idle time preserved by the overflow would range between [period/2,period-1].) Signed-off-by: Paul Turner <pjt@google.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <20110122044852.102126037@google.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
-rw-r--r--kernel/sched.c2
-rw-r--r--kernel/sched_fair.c1
2 files changed, 3 insertions, 0 deletions
diff --git a/kernel/sched.c b/kernel/sched.c
index e0fa3ff7f19..6820b5b3a96 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -7796,6 +7796,8 @@ static void init_cfs_rq(struct cfs_rq *cfs_rq, struct rq *rq)
INIT_LIST_HEAD(&cfs_rq->tasks);
#ifdef CONFIG_FAIR_GROUP_SCHED
cfs_rq->rq = rq;
+ /* allow initial update_cfs_load() to truncate */
+ cfs_rq->load_stamp = 1;
#endif
cfs_rq->min_vruntime = (u64)(-(1LL << 20));
}
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 0c550c841ee..4cbc9121094 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -733,6 +733,7 @@ static void update_cfs_load(struct cfs_rq *cfs_rq, int global_update)
now - cfs_rq->load_last > 4 * period) {
cfs_rq->load_period = 0;
cfs_rq->load_avg = 0;
+ delta = period - 1;
}
cfs_rq->load_stamp = now;