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Commit a021dc03 authored by Gautham R Shenoy's avatar Gautham R Shenoy Committed by Ingo Molnar
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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: default avatarGautham R Shenoy <ego@in.ibm.com>
Acked-by: default avatarPeter 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: default avatarIngo Molnar <mingo@elte.hu>
parent dbc523a3

kernel/sched.c

+14 −9
Original line number Diff line number Diff line
@@ -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)

	/*

	 * 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)