Messages in this thread Patch in this message | | | Date | Wed, 26 Jan 2011 12:11:28 GMT | From | tip-bot for Paul Turner <> | Subject | [tip:sched/core] sched: Avoid expensive initial update_cfs_load() |
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Commit-ID: f07333bf6ee66d9b49286cec4371cf375e745b7a Gitweb: http://git.kernel.org/tip/f07333bf6ee66d9b49286cec4371cf375e745b7a Author: Paul Turner <pjt@google.com> AuthorDate: Fri, 21 Jan 2011 20:45:03 -0800 Committer: Ingo Molnar <mingo@elte.hu> CommitDate: Wed, 26 Jan 2011 12:33:19 +0100
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> --- kernel/sched.c | 2 ++ kernel/sched_fair.c | 1 + 2 files changed, 3 insertions(+), 0 deletions(-)
diff --git a/kernel/sched.c b/kernel/sched.c index e0fa3ff..6820b5b 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 0c550c8..4cbc912 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;
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