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Subject[tip:sched/balancing] sched: Optimize the !power_savings_balance during fbg()
Commit-ID:  a021dc03376707c55a3483e32c16b8986d4414cc
Gitweb: http://git.kernel.org/tip/a021dc03376707c55a3483e32c16b8986d4414cc
Author: Gautham R Shenoy <ego@in.ibm.com>
AuthorDate: Wed, 25 Mar 2009 14:44:17 +0530
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Wed, 25 Mar 2009 10:30:48 +0100

sched: Optimize the !power_savings_balance during fbg()

Impact: cleanup, micro-optimization

We don't need to perform power_savings balance if either the
cpu is NOT_IDLE or if the sched_domain doesn't contain the
SD_POWERSAVINGS_BALANCE flag set.

Currently, we check for these conditions multiple number of
times, even though these variables don't change over the scope
of find_busiest_group().

Check once, and store the value in the already exiting
"power_savings_balance" variable.

Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: "Balbir Singh" <balbir@in.ibm.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: "Dhaval Giani" <dhaval@linux.vnet.ibm.com>
Cc: Bharata B Rao <bharata@linux.vnet.ibm.com>
Cc: "Vaidyanathan Srinivasan" <svaidy@linux.vnet.ibm.com>
LKML-Reference: <20090325091417.13992.2657.stgit@sofia.in.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>


---
kernel/sched.c | 23 ++++++++++++++---------
1 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 934f615..71e8dca 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3386,8 +3386,17 @@ static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu,
int load_idx;

#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
- sds->power_savings_balance = 1;
- sds->min_nr_running = ULONG_MAX;
+ /*
+ * Busy processors will not participate in power savings
+ * balance.
+ */
+ if (idle == CPU_NOT_IDLE || !(sd->flags & SD_POWERSAVINGS_BALANCE))
+ sds->power_savings_balance = 0;
+ else {
+ sds->power_savings_balance = 1;
+ sds->min_nr_running = ULONG_MAX;
+ sds->leader_nr_running = 0;
+ }
#endif
load_idx = get_sd_load_idx(sd, idle);

@@ -3422,12 +3431,8 @@ static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu,
}

#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
- /*
- * Busy processors will not participate in power savings
- * balance.
- */
- if (idle == CPU_NOT_IDLE ||
- !(sd->flags & SD_POWERSAVINGS_BALANCE))
+
+ if (!sds->power_savings_balance)
goto group_next;

/*
@@ -3651,7 +3656,7 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,

out_balanced:
#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
- if (idle == CPU_NOT_IDLE || !(sd->flags & SD_POWERSAVINGS_BALANCE))
+ if (!sds.power_savings_balance)
goto ret;

if (sds.this != sds.group_leader || sds.group_leader == sds.group_min)

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