Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760218AbZCYJvL (ORCPT ); Wed, 25 Mar 2009 05:51:11 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759613AbZCYJsJ (ORCPT ); Wed, 25 Mar 2009 05:48:09 -0400 Received: from hera.kernel.org ([140.211.167.34]:46509 "EHLO hera.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759595AbZCYJsH (ORCPT ); Wed, 25 Mar 2009 05:48:07 -0400 Date: Wed, 25 Mar 2009 09:47:16 GMT From: Gautham R Shenoy To: linux-tip-commits@vger.kernel.org Cc: linux-kernel@vger.kernel.org, ego@in.ibm.com, hpa@zytor.com, mingo@redhat.com, a.p.zijlstra@chello.nl, dhaval@linux.vnet.ibm.com, balbir@in.ibm.com, bharata@linux.vnet.ibm.com, suresh.b.siddha@intel.com, tglx@linutronix.de, mingo@elte.hu, svaidy@linux.vnet.ibm.com, nickpiggin@yahoo.com.au Reply-To: mingo@redhat.com, hpa@zytor.com, ego@in.ibm.com, linux-kernel@vger.kernel.org, a.p.zijlstra@chello.nl, dhaval@linux.vnet.ibm.com, balbir@in.ibm.com, bharata@linux.vnet.ibm.com, suresh.b.siddha@intel.com, tglx@linutronix.de, nickpiggin@yahoo.com.au, svaidy@linux.vnet.ibm.com, mingo@elte.hu In-Reply-To: <20090325091427.13992.18933.stgit@sofia.in.ibm.com> References: <20090325091427.13992.18933.stgit@sofia.in.ibm.com> Subject: [tip:sched/balancing] sched: Add comments to find_busiest_group() function Message-ID: Git-Commit-ID: 7b6340ef884aff69a54f8a530c73ad9da0a7c388 X-Mailer: tip-git-log-daemon MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.0 (hera.kernel.org [127.0.0.1]); Wed, 25 Mar 2009 09:47:18 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4490 Lines: 113 Commit-ID: 7b6340ef884aff69a54f8a530c73ad9da0a7c388 Gitweb: http://git.kernel.org/tip/7b6340ef884aff69a54f8a530c73ad9da0a7c388 Author: Gautham R Shenoy AuthorDate: Wed, 25 Mar 2009 14:44:27 +0530 Committer: Ingo Molnar CommitDate: Wed, 25 Mar 2009 10:30:49 +0100 sched: Add comments to find_busiest_group() function Impact: cleanup Add /** style comments around find_busiest_group(). Also add a few explanatory comments. This concludes the find_busiest_group() cleanup. The function is now down to 72 lines from the original 313 lines. Signed-off-by: Gautham R Shenoy Acked-by: Peter Zijlstra Cc: Suresh Siddha Cc: "Balbir Singh" Cc: Nick Piggin Cc: "Dhaval Giani" Cc: Bharata B Rao Cc: "Vaidyanathan Srinivasan" LKML-Reference: <20090325091427.13992.18933.stgit@sofia.in.ibm.com> Signed-off-by: Ingo Molnar --- kernel/sched.c | 50 ++++++++++++++++++++++++++++++++++++++++++-------- 1 files changed, 42 insertions(+), 8 deletions(-) diff --git a/kernel/sched.c b/kernel/sched.c index 5f21658..b7723bd 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -3676,10 +3676,30 @@ static inline void calculate_imbalance(struct sd_lb_stats *sds, int this_cpu, } /******* find_busiest_group() helpers end here *********************/ -/* - * find_busiest_group finds and returns the busiest CPU group within the - * domain. It calculates and returns the amount of weighted load which - * should be moved to restore balance via the imbalance parameter. +/** + * find_busiest_group - Returns the busiest group within the sched_domain + * if there is an imbalance. If there isn't an imbalance, and + * the user has opted for power-savings, it returns a group whose + * CPUs can be put to idle by rebalancing those tasks elsewhere, if + * such a group exists. + * + * Also calculates the amount of weighted load which should be moved + * to restore balance. + * + * @sd: The sched_domain whose busiest group is to be returned. + * @this_cpu: The cpu for which load balancing is currently being performed. + * @imbalance: Variable which stores amount of weighted load which should + * be moved to restore balance/put a group to idle. + * @idle: The idle status of this_cpu. + * @sd_idle: The idleness of sd + * @cpus: The set of CPUs under consideration for load-balancing. + * @balance: Pointer to a variable indicating if this_cpu + * is the appropriate cpu to perform load balancing at this_level. + * + * Returns: - the busiest group if imbalance exists. + * - If no imbalance and user has opted for power-savings balance, + * return the least loaded group whose CPUs can be + * put to idle by rebalancing its tasks onto our group. */ static struct sched_group * find_busiest_group(struct sched_domain *sd, int this_cpu, @@ -3697,17 +3717,31 @@ find_busiest_group(struct sched_domain *sd, int this_cpu, update_sd_lb_stats(sd, this_cpu, idle, sd_idle, cpus, balance, &sds); + /* Cases where imbalance does not exist from POV of this_cpu */ + /* 1) this_cpu is not the appropriate cpu to perform load balancing + * at this level. + * 2) There is no busy sibling group to pull from. + * 3) This group is the busiest group. + * 4) This group is more busy than the avg busieness at this + * sched_domain. + * 5) The imbalance is within the specified limit. + * 6) Any rebalance would lead to ping-pong + */ if (balance && !(*balance)) goto ret; - if (!sds.busiest || sds.this_load >= sds.max_load - || sds.busiest_nr_running == 0) + if (!sds.busiest || sd.busiest_nr_running == 0) + goto out_balanced; + + if (sds.this_load >= sds.max_load) goto out_balanced; sds.avg_load = (SCHED_LOAD_SCALE * sds.total_load) / sds.total_pwr; - if (sds.this_load >= sds.avg_load || - 100*sds.max_load <= sd->imbalance_pct * sds.this_load) + if (sds.this_load >= sds.avg_load) + goto out_balanced; + + if (100 * sds.max_load <= sd->imbalance_pct * sds.this_load) goto out_balanced; sds.busiest_load_per_task /= sds.busiest_nr_running; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/