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Message-ID: <20090325114314.GC11302@in.ibm.com> Date: Wed, 25 Mar 2009 17:13:14 +0530 From: Gautham R Shenoy <ego@...ibm.com> To: Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com> Cc: linux-kernel@...r.kernel.org, Suresh Siddha <suresh.b.siddha@...el.com>, Balbir Singh <balbir@...ibm.com>, Nick Piggin <nickpiggin@...oo.com.au>, Dhaval Giani <dhaval@...ux.vnet.ibm.com>, Bharata B Rao <bharata@...ux.vnet.ibm.com> Subject: Re: [RFC PATCH 11/11] sched: Add comments to find_busiest_group() function. On Wed, Mar 25, 2009 at 02:44:27PM +0530, Gautham R Shenoy wrote: > Add /** style comments around find_busiest_group(). Also add a few explanatory > */ <snip> > static struct sched_group * > find_busiest_group(struct sched_domain *sd, int this_cpu, > @@ -3593,17 +3613,31 @@ 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) ^^^^^^^^^^^^^^^^^^^^ should have been sds.busiest_nr_running. Hence the build failure on tip. I think I missed compile testing this last patch. Ingo, could you revert commit 7b6340ef884aff69a54f8a530c73ad9da0a7c388 in tip/balancing and commit the following patch instead? ---> sched: Add comments to find_busiest_group() function. From: Gautham R Shenoy <ego@...ibm.com> Add /** style comments around find_busiest_group(). Also add a few explanatory comments. This concludes the find_busiest_group() cleanup. The function is down to 72 lines from the original 313 lines. Signed-off-by: Gautham R Shenoy <ego@...ibm.com> --- kernel/sched.c | 50 ++++++++++++++++++++++++++++++++++++++++++-------- 1 files changed, 42 insertions(+), 8 deletions(-) diff --git a/kernel/sched.c b/kernel/sched.c index 6404ddf..a48cf9d 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -3572,10 +3572,30 @@ 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, @@ -3593,17 +3613,31 @@ 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 || sds.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; -- Thanks and Regards gautham -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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