[PATCH 0/3] sched: asymmetrical packing for POWER7 SMT4

[PATCH 0/3] sched: asymmetrical packing for POWER7 SMT4

[Michael Neuling]

This patch series implements asymmetric SMT packing which ensures
consistently good performance on POWER7.  Without this series, tasks
will vary in performance by around +/-30% on POWER7

This new version is based on help from Vatsa and Vaidy in an attempt
to answer concerns that Peter Zijlstra had about the original series.

The 1st patch is a fix for SMT4 in general.
The 2nd adds actual the asymmetrical packing infrastructure.  
The 3rd adds the powerpc specific hooks for POWER7.

[PATCH 2/3] sched: add asymmetric group packing option for sibling domain

[Michael Neuling]

Check to see if the group is packed in a sched doman.

This is primarily intended to used at the sibling level.  Some cores
like POWER7 prefer to use lower numbered SMT threads.  In the case of
POWER7, it can move to lower SMT modes only when higher threads are
idle.  When in lower SMT modes, the threads will perform better since
they share less core resources.  Hence when we have idle threads, we
want them to be the higher ones.

This adds a hook into f_b_g() called check_asym_packing() to check the
packing.  This packing function is run on idle threads.  It checks to
see if the busiest CPU in this domain (core in the P7 case) has a
higher CPU number than what where the packing function is being run
on.  If it is, calculate the imbalance and return the higher busier
thread as the busiest group to f_b_g().  Here we are assuming a lower
CPU number will be equivalent to a lower SMT thread number.

It also creates a new SD_ASYM_PACKING flag to enable this feature at
any scheduler domain level.

It also creates an arch hook to enable this feature at the sibling
level.  The default function doesn't enable this feature.

Based heavily on patch from Peter Zijlstra.  
Fixes from Srivatsa Vaddagiri.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>

---

 include/linux/sched.h    |    4 +
 include/linux/topology.h |    1 
 kernel/sched_fair.c      |  104 +++++++++++++++++++++++++++++++++++++++++++++--
 3 files changed, 104 insertions(+), 5 deletions(-)

Index: linux-2.6-ozlabs/include/linux/sched.h
===================================================================
--- linux-2.6-ozlabs.orig/include/linux/sched.h
+++ linux-2.6-ozlabs/include/linux/sched.h
@@ -804,7 +804,7 @@ enum cpu_idle_type {
 #define SD_POWERSAVINGS_BALANCE	0x0100	/* Balance for power savings */
 #define SD_SHARE_PKG_RESOURCES	0x0200	/* Domain members share cpu pkg resources */
 #define SD_SERIALIZE		0x0400	/* Only a single load balancing instance */
-
+#define SD_ASYM_PACKING		0x0800  /* Place busy groups earlier in the domain */
 #define SD_PREFER_SIBLING	0x1000	/* Prefer to place tasks in a sibling domain */
 
 enum powersavings_balance_level {
@@ -839,6 +839,8 @@ static inline int sd_balance_for_package
 	return SD_PREFER_SIBLING;
 }
 
+extern int __weak arch_sd_sibiling_asym_packing(void);
+
 /*
  * Optimise SD flags for power savings:
  * SD_BALANCE_NEWIDLE helps agressive task consolidation and power savings.
Index: linux-2.6-ozlabs/include/linux/topology.h
===================================================================
--- linux-2.6-ozlabs.orig/include/linux/topology.h
+++ linux-2.6-ozlabs/include/linux/topology.h
@@ -103,6 +103,7 @@ int arch_update_cpu_topology(void);
 				| 1*SD_SHARE_PKG_RESOURCES		\
 				| 0*SD_SERIALIZE			\
 				| 0*SD_PREFER_SIBLING			\
+				| arch_sd_sibiling_asym_packing()	\
 				,					\
 	.last_balance		= jiffies,				\
 	.balance_interval	= 1,					\
Index: linux-2.6-ozlabs/kernel/sched_fair.c
===================================================================
--- linux-2.6-ozlabs.orig/kernel/sched_fair.c
+++ linux-2.6-ozlabs/kernel/sched_fair.c
@@ -2463,6 +2463,41 @@ static inline void update_sg_lb_stats(st
 }
 
 /**
+ * update_sd_pick_busiest - return 1 on busiest group
+ * @sd: sched_domain whose statistics are to be checked
+ * @sds: sched_domain statistics
+ * @sg: sched_group candidate to be checked for being the busiest
+ * @sds: sched_group statistics
+ *
+ * This returns 1 for the busiest group. If asymmetric packing is
+ * enabled and we already have a busiest, but this candidate group has
+ * a higher cpu number than the current busiest, pick this sg.
+ */
+static int update_sd_pick_busiest(struct sched_domain *sd,
+				  struct sd_lb_stats *sds,
+				  struct sched_group *sg,
+				  struct sg_lb_stats *sgs,
+				  int this_cpu)
+{
+	if (sgs->sum_nr_running > sgs->group_capacity)
+		return 1;
+
+	if (sgs->group_imb)
+		return 1;
+
+	if ((sd->flags & SD_ASYM_PACKING) && sgs->sum_nr_running &&
+	    this_cpu < group_first_cpu(sg)) {
+		if (!sds->busiest)
+			return 1;
+
+		if (group_first_cpu(sds->busiest) > group_first_cpu(sg))
+			return 1;
+	}
+
+	return 0;
+}
+
+/**
  * update_sd_lb_stats - Update sched_group's statistics for load balancing.
  * @sd: sched_domain whose statistics are to be updated.
  * @this_cpu: Cpu for which load balance is currently performed.
@@ -2517,8 +2552,8 @@ static inline void update_sd_lb_stats(st
 			sds->this_nr_running = sgs.sum_nr_running;
 			sds->this_load_per_task = sgs.sum_weighted_load;
 		} else if (sgs.avg_load > sds->max_load &&
-			   (sgs.sum_nr_running > sgs.group_capacity ||
-				sgs.group_imb)) {
+			   update_sd_pick_busiest(sd, sds, group, &sgs,
+						  this_cpu)) {
 			sds->max_load = sgs.avg_load;
 			sds->busiest = group;
 			sds->busiest_nr_running = sgs.sum_nr_running;
@@ -2532,6 +2567,57 @@ static inline void update_sd_lb_stats(st
 	} while (group != sd->groups);
 }
 
+int __weak arch_sd_sibiling_asym_packing(void)
+{
+       return 0*SD_ASYM_PACKING;
+}
+
+/**
+ * check_asym_packing - Check to see if the group is packed into the
+ *			sched doman.
+ *
+ * This is primarily intended to used at the sibling level.  Some
+ * cores like POWER7 prefer to use lower numbered SMT threads.  In the
+ * case of POWER7, it can move to lower SMT modes only when higher
+ * threads are idle.  When in lower SMT modes, the threads will
+ * perform better since they share less core resources.  Hence when we
+ * have idle threads, we want them to be the higher ones.
+ *
+ * This packing function is run on idle threads.  It checks to see if
+ * the busiest CPU in this domain (core in the P7 case) has a higher
+ * CPU number than the packing function is being run on.  Here we are
+ * assuming lower CPU number will be equivalent to lower a SMT thread
+ * number.
+ *
+ * @sd: The sched_domain whose packing is to be checked.
+ * @sds: Statistics of the sched_domain which is to be packed
+ * @this_cpu: The cpu at whose sched_domain we're performing load-balance.
+ * @imbalance: returns amount of imbalanced due to packing.
+ *
+ * Returns 1 when packing is required and a task should be moved to
+ * this CPU.  The amount of the imbalance is returned in *imbalance.
+ */
+static int check_asym_packing(struct sched_domain *sd,
+			      struct sd_lb_stats *sds,
+			      int this_cpu, unsigned long *imbalance)
+{
+	int busiest_cpu;
+
+	if (!(sd->flags & SD_ASYM_PACKING))
+		return 0;
+
+	if (!sds->busiest)
+		return 0;
+
+	busiest_cpu = group_first_cpu(sds->busiest);
+	if (this_cpu > busiest_cpu)
+		return 0;
+
+	*imbalance = DIV_ROUND_CLOSEST(sds->max_load * sds->busiest->cpu_power,
+				       SCHED_LOAD_SCALE);
+	return 1;
+}
+
 /**
  * fix_small_imbalance - Calculate the minor imbalance that exists
  *			amongst the groups of a sched_domain, during
@@ -2724,6 +2810,10 @@ find_busiest_group(struct sched_domain *
 	if (!(*balance))
 		goto ret;
 
+	if ((idle == CPU_IDLE || idle == CPU_NEWLY_IDLE) &&
+	    check_asym_packing(sd, &sds, this_cpu, imbalance))
+		return sds.busiest;
+
 	if (!sds.busiest || sds.busiest_nr_running == 0)
 		goto out_balanced;
 
@@ -2813,9 +2903,14 @@ find_busiest_queue(struct sched_group *g
 /* Working cpumask for load_balance and load_balance_newidle. */
 static DEFINE_PER_CPU(cpumask_var_t, load_balance_tmpmask);
 
-static int need_active_balance(struct sched_domain *sd, int sd_idle, int idle)
+static int need_active_balance(struct sched_domain *sd, int sd_idle, int idle,
+			       int busiest_cpu, int this_cpu)
 {
 	if (idle == CPU_NEWLY_IDLE) {
+
+		if (sd->flags & SD_ASYM_PACKING && busiest_cpu > this_cpu)
+			return 1;
+
 		/*
 		 * The only task running in a non-idle cpu can be moved to this
 		 * cpu in an attempt to completely freeup the other CPU
@@ -2934,7 +3029,8 @@ redo:
 		schedstat_inc(sd, lb_failed[idle]);
 		sd->nr_balance_failed++;
 
-		if (need_active_balance(sd, sd_idle, idle)) {
+		if (need_active_balance(sd, sd_idle, idle, cpu_of(busiest),
+					this_cpu)) {
 			raw_spin_lock_irqsave(&busiest->lock, flags);
 
 			/* don't kick the active_load_balance_cpu_stop,

[tip:sched/core] sched: Add asymmetric group packing option for sibling domain

[tip-bot for Michael Neuling]

Commit-ID:  532cb4c401e225b084c14d6bd6a2f8ee561de2f1
Gitweb:     http://git.kernel.org/tip/532cb4c401e225b084c14d6bd6a2f8ee561de2f1
Author:     Michael Neuling <mikey@neuling.org>
AuthorDate: Tue, 8 Jun 2010 14:57:02 +1000
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Wed, 9 Jun 2010 10:34:55 +0200

sched: Add asymmetric group packing option for sibling domain

Check to see if the group is packed in a sched doman.

This is primarily intended to used at the sibling level.  Some cores
like POWER7 prefer to use lower numbered SMT threads.  In the case of
POWER7, it can move to lower SMT modes only when higher threads are
idle.  When in lower SMT modes, the threads will perform better since
they share less core resources.  Hence when we have idle threads, we
want them to be the higher ones.

This adds a hook into f_b_g() called check_asym_packing() to check the
packing.  This packing function is run on idle threads.  It checks to
see if the busiest CPU in this domain (core in the P7 case) has a
higher CPU number than what where the packing function is being run
on.  If it is, calculate the imbalance and return the higher busier
thread as the busiest group to f_b_g().  Here we are assuming a lower
CPU number will be equivalent to a lower SMT thread number.

It also creates a new SD_ASYM_PACKING flag to enable this feature at
any scheduler domain level.

It also creates an arch hook to enable this feature at the sibling
level.  The default function doesn't enable this feature.

Based heavily on patch from Peter Zijlstra.
Fixes from Srivatsa Vaddagiri.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
LKML-Reference: <20100608045702.2936CCC897@localhost.localdomain>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 include/linux/sched.h    |    4 +-
 include/linux/topology.h |    1 +
 kernel/sched_fair.c      |  139 ++++++++++++++++++++++++++++++++++++++++------
 3 files changed, 126 insertions(+), 18 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index c731296..ff154e1 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -801,7 +801,7 @@ enum cpu_idle_type {
 #define SD_POWERSAVINGS_BALANCE	0x0100	/* Balance for power savings */
 #define SD_SHARE_PKG_RESOURCES	0x0200	/* Domain members share cpu pkg resources */
 #define SD_SERIALIZE		0x0400	/* Only a single load balancing instance */
-
+#define SD_ASYM_PACKING		0x0800  /* Place busy groups earlier in the domain */
 #define SD_PREFER_SIBLING	0x1000	/* Prefer to place tasks in a sibling domain */
 
 enum powersavings_balance_level {
@@ -836,6 +836,8 @@ static inline int sd_balance_for_package_power(void)
 	return SD_PREFER_SIBLING;
 }
 
+extern int __weak arch_sd_sibiling_asym_packing(void);
+
 /*
  * Optimise SD flags for power savings:
  * SD_BALANCE_NEWIDLE helps agressive task consolidation and power savings.
diff --git a/include/linux/topology.h b/include/linux/topology.h
index c44df50..cf57f30 100644
--- a/include/linux/topology.h
+++ b/include/linux/topology.h
@@ -103,6 +103,7 @@ int arch_update_cpu_topology(void);
 				| 1*SD_SHARE_PKG_RESOURCES		\
 				| 0*SD_SERIALIZE			\
 				| 0*SD_PREFER_SIBLING			\
+				| arch_sd_sibiling_asym_packing()	\
 				,					\
 	.last_balance		= jiffies,				\
 	.balance_interval	= 1,					\
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index b9b3462..593424f 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -2458,11 +2458,53 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
 }
 
 /**
+ * update_sd_pick_busiest - return 1 on busiest group
+ * @sd: sched_domain whose statistics are to be checked
+ * @sds: sched_domain statistics
+ * @sg: sched_group candidate to be checked for being the busiest
+ * @sds: sched_group statistics
+ *
+ * Determine if @sg is a busier group than the previously selected
+ * busiest group.
+ */
+static bool update_sd_pick_busiest(struct sched_domain *sd,
+				   struct sd_lb_stats *sds,
+				   struct sched_group *sg,
+				   struct sg_lb_stats *sgs,
+				   int this_cpu)
+{
+	if (sgs->avg_load <= sds->max_load)
+		return false;
+
+	if (sgs->sum_nr_running > sgs->group_capacity)
+		return true;
+
+	if (sgs->group_imb)
+		return true;
+
+	/*
+	 * ASYM_PACKING needs to move all the work to the lowest
+	 * numbered CPUs in the group, therefore mark all groups
+	 * higher than ourself as busy.
+	 */
+	if ((sd->flags & SD_ASYM_PACKING) && sgs->sum_nr_running &&
+	    this_cpu < group_first_cpu(sg)) {
+		if (!sds->busiest)
+			return true;
+
+		if (group_first_cpu(sds->busiest) > group_first_cpu(sg))
+			return true;
+	}
+
+	return false;
+}
+
+/**
  * update_sd_lb_stats - Update sched_group's statistics for load balancing.
  * @sd: sched_domain whose statistics are to be updated.
  * @this_cpu: Cpu for which load balance is currently performed.
  * @idle: Idle status of this_cpu
- * @sd_idle: Idle status of the sched_domain containing group.
+ * @sd_idle: Idle status of the sched_domain containing sg.
  * @cpus: Set of cpus considered for load balancing.
  * @balance: Should we balance.
  * @sds: variable to hold the statistics for this sched_domain.
@@ -2473,7 +2515,7 @@ static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu,
 			struct sd_lb_stats *sds)
 {
 	struct sched_domain *child = sd->child;
-	struct sched_group *group = sd->groups;
+	struct sched_group *sg = sd->groups;
 	struct sg_lb_stats sgs;
 	int load_idx, prefer_sibling = 0;
 
@@ -2486,21 +2528,20 @@ static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu,
 	do {
 		int local_group;
 
-		local_group = cpumask_test_cpu(this_cpu,
-					       sched_group_cpus(group));
+		local_group = cpumask_test_cpu(this_cpu, sched_group_cpus(sg));
 		memset(&sgs, 0, sizeof(sgs));
-		update_sg_lb_stats(sd, group, this_cpu, idle, load_idx, sd_idle,
+		update_sg_lb_stats(sd, sg, this_cpu, idle, load_idx, sd_idle,
 				local_group, cpus, balance, &sgs);
 
 		if (local_group && !(*balance))
 			return;
 
 		sds->total_load += sgs.group_load;
-		sds->total_pwr += group->cpu_power;
+		sds->total_pwr += sg->cpu_power;
 
 		/*
 		 * In case the child domain prefers tasks go to siblings
-		 * first, lower the group capacity to one so that we'll try
+		 * first, lower the sg capacity to one so that we'll try
 		 * and move all the excess tasks away.
 		 */
 		if (prefer_sibling)
@@ -2508,23 +2549,72 @@ static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu,
 
 		if (local_group) {
 			sds->this_load = sgs.avg_load;
-			sds->this = group;
+			sds->this = sg;
 			sds->this_nr_running = sgs.sum_nr_running;
 			sds->this_load_per_task = sgs.sum_weighted_load;
-		} else if (sgs.avg_load > sds->max_load &&
-			   (sgs.sum_nr_running > sgs.group_capacity ||
-				sgs.group_imb)) {
+		} else if (update_sd_pick_busiest(sd, sds, sg, &sgs, this_cpu)) {
 			sds->max_load = sgs.avg_load;
-			sds->busiest = group;
+			sds->busiest = sg;
 			sds->busiest_nr_running = sgs.sum_nr_running;
 			sds->busiest_group_capacity = sgs.group_capacity;
 			sds->busiest_load_per_task = sgs.sum_weighted_load;
 			sds->group_imb = sgs.group_imb;
 		}
 
-		update_sd_power_savings_stats(group, sds, local_group, &sgs);
-		group = group->next;
-	} while (group != sd->groups);
+		update_sd_power_savings_stats(sg, sds, local_group, &sgs);
+		sg = sg->next;
+	} while (sg != sd->groups);
+}
+
+int __weak arch_sd_sibiling_asym_packing(void)
+{
+       return 0*SD_ASYM_PACKING;
+}
+
+/**
+ * check_asym_packing - Check to see if the group is packed into the
+ *			sched doman.
+ *
+ * This is primarily intended to used at the sibling level.  Some
+ * cores like POWER7 prefer to use lower numbered SMT threads.  In the
+ * case of POWER7, it can move to lower SMT modes only when higher
+ * threads are idle.  When in lower SMT modes, the threads will
+ * perform better since they share less core resources.  Hence when we
+ * have idle threads, we want them to be the higher ones.
+ *
+ * This packing function is run on idle threads.  It checks to see if
+ * the busiest CPU in this domain (core in the P7 case) has a higher
+ * CPU number than the packing function is being run on.  Here we are
+ * assuming lower CPU number will be equivalent to lower a SMT thread
+ * number.
+ *
+ * @sd: The sched_domain whose packing is to be checked.
+ * @sds: Statistics of the sched_domain which is to be packed
+ * @this_cpu: The cpu at whose sched_domain we're performing load-balance.
+ * @imbalance: returns amount of imbalanced due to packing.
+ *
+ * Returns 1 when packing is required and a task should be moved to
+ * this CPU.  The amount of the imbalance is returned in *imbalance.
+ */
+static int check_asym_packing(struct sched_domain *sd,
+			      struct sd_lb_stats *sds,
+			      int this_cpu, unsigned long *imbalance)
+{
+	int busiest_cpu;
+
+	if (!(sd->flags & SD_ASYM_PACKING))
+		return 0;
+
+	if (!sds->busiest)
+		return 0;
+
+	busiest_cpu = group_first_cpu(sds->busiest);
+	if (this_cpu > busiest_cpu)
+		return 0;
+
+	*imbalance = DIV_ROUND_CLOSEST(sds->max_load * sds->busiest->cpu_power,
+				       SCHED_LOAD_SCALE);
+	return 1;
 }
 
 /**
@@ -2719,6 +2809,10 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
 	if (!(*balance))
 		goto ret;
 
+	if ((idle == CPU_IDLE || idle == CPU_NEWLY_IDLE) &&
+	    check_asym_packing(sd, &sds, this_cpu, imbalance))
+		return sds.busiest;
+
 	if (!sds.busiest || sds.busiest_nr_running == 0)
 		goto out_balanced;
 
@@ -2808,9 +2902,19 @@ find_busiest_queue(struct sched_domain *sd, struct sched_group *group,
 /* Working cpumask for load_balance and load_balance_newidle. */
 static DEFINE_PER_CPU(cpumask_var_t, load_balance_tmpmask);
 
-static int need_active_balance(struct sched_domain *sd, int sd_idle, int idle)
+static int need_active_balance(struct sched_domain *sd, int sd_idle, int idle,
+			       int busiest_cpu, int this_cpu)
 {
 	if (idle == CPU_NEWLY_IDLE) {
+
+		/*
+		 * ASYM_PACKING needs to force migrate tasks from busy but
+		 * higher numbered CPUs in order to pack all tasks in the
+		 * lowest numbered CPUs.
+		 */
+		if ((sd->flags & SD_ASYM_PACKING) && busiest_cpu > this_cpu)
+			return 1;
+
 		/*
 		 * The only task running in a non-idle cpu can be moved to this
 		 * cpu in an attempt to completely freeup the other CPU
@@ -2929,7 +3033,8 @@ redo:
 		schedstat_inc(sd, lb_failed[idle]);
 		sd->nr_balance_failed++;
 
-		if (need_active_balance(sd, sd_idle, idle)) {
+		if (need_active_balance(sd, sd_idle, idle, cpu_of(busiest),
+					this_cpu)) {
 			raw_spin_lock_irqsave(&busiest->lock, flags);
 
 			/* don't kick the active_load_balance_cpu_stop,

[PATCH 3/3] powerpc: enabled asymmetric SMT scheduling on POWER7

[Michael Neuling]

The POWER7 core has dynamic SMT mode switching which is controlled by
the hypervisor.  There are 3 SMT modes:
	SMT1 uses thread  0
	SMT2 uses threads 0 & 1
	SMT4 uses threads 0, 1, 2 & 3
When in any particular SMT mode, all threads have the same performance
as each other (ie. at any moment in time, all threads perform the same).  

The SMT mode switching works such that when linux has threads 2 & 3 idle
and 0 & 1 active, it will cede (H_CEDE hypercall) threads 2 and 3 in the
idle loop and the hypervisor will automatically switch to SMT2 for that
core (independent of other cores).  The opposite is not true, so if
threads 0 & 1 are idle and 2 & 3 are active, we will stay in SMT4 mode.

Similarly if thread 0 is active and threads 1, 2 & 3 are idle, we'll go
into SMT1 mode.  

If we can get the core into a lower SMT mode (SMT1 is best), the threads
will perform better (since they share less core resources).  Hence when
we have idle threads, we want them to be the higher ones.

This adds a feature bit for asymmetric packing to powerpc and then
enables it on POWER7. 

Signed-off-by: Michael Neuling <mikey@neuling.org>

---

 arch/powerpc/include/asm/cputable.h |    3 ++-
 arch/powerpc/kernel/process.c       |    9 +++++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

Index: linux-2.6-ozlabs/arch/powerpc/include/asm/cputable.h
===================================================================
--- linux-2.6-ozlabs.orig/arch/powerpc/include/asm/cputable.h
+++ linux-2.6-ozlabs/arch/powerpc/include/asm/cputable.h
@@ -195,6 +195,7 @@ extern const char *powerpc_base_platform
 #define CPU_FTR_SAO			LONG_ASM_CONST(0x0020000000000000)
 #define CPU_FTR_CP_USE_DCBTZ		LONG_ASM_CONST(0x0040000000000000)
 #define CPU_FTR_UNALIGNED_LD_STD	LONG_ASM_CONST(0x0080000000000000)
+#define CPU_FTR_ASYM_SMT		LONG_ASM_CONST(0x0100000000000000)
 
 #ifndef __ASSEMBLY__
 
@@ -409,7 +410,7 @@ extern const char *powerpc_base_platform
 	    CPU_FTR_MMCRA | CPU_FTR_SMT | \
 	    CPU_FTR_COHERENT_ICACHE | CPU_FTR_LOCKLESS_TLBIE | \
 	    CPU_FTR_PURR | CPU_FTR_SPURR | CPU_FTR_REAL_LE | \
-	    CPU_FTR_DSCR | CPU_FTR_SAO)
+	    CPU_FTR_DSCR | CPU_FTR_SAO  | CPU_FTR_ASYM_SMT)
 #define CPU_FTRS_CELL	(CPU_FTR_USE_TB | CPU_FTR_LWSYNC | \
 	    CPU_FTR_PPCAS_ARCH_V2 | CPU_FTR_CTRL | \
 	    CPU_FTR_ALTIVEC_COMP | CPU_FTR_MMCRA | CPU_FTR_SMT | \
Index: linux-2.6-ozlabs/arch/powerpc/kernel/process.c
===================================================================
--- linux-2.6-ozlabs.orig/arch/powerpc/kernel/process.c
+++ linux-2.6-ozlabs/arch/powerpc/kernel/process.c
@@ -1265,3 +1265,12 @@ unsigned long randomize_et_dyn(unsigned 
 
 	return ret;
 }
+
+int arch_sd_sibiling_asym_packing(void)
+{
+	if (cpu_has_feature(CPU_FTR_ASYM_SMT)){
+		printk_once(KERN_INFO "Enabling Asymmetric SMT scheduling\n");
+		return SD_ASYM_PACKING;
+	}
+	return 0;
+}

Re: [PATCH 3/3] powerpc: enabled asymmetric SMT scheduling on POWER7

[Benjamin Herrenschmidt]

On Tue, 2010-06-08 at 14:57 +1000, Michael Neuling wrote:
> The POWER7 core has dynamic SMT mode switching which is controlled by
> the hypervisor.  There are 3 SMT modes:
> 	SMT1 uses thread  0
> 	SMT2 uses threads 0 & 1
> 	SMT4 uses threads 0, 1, 2 & 3
> When in any particular SMT mode, all threads have the same performance
> as each other (ie. at any moment in time, all threads perform the same).  
> 
> The SMT mode switching works such that when linux has threads 2 & 3 idle
> and 0 & 1 active, it will cede (H_CEDE hypercall) threads 2 and 3 in the
> idle loop and the hypervisor will automatically switch to SMT2 for that
> core (independent of other cores).  The opposite is not true, so if
> threads 0 & 1 are idle and 2 & 3 are active, we will stay in SMT4 mode.
> 
> Similarly if thread 0 is active and threads 1, 2 & 3 are idle, we'll go
> into SMT1 mode.  
> 
> If we can get the core into a lower SMT mode (SMT1 is best), the threads
> will perform better (since they share less core resources).  Hence when
> we have idle threads, we want them to be the higher ones.
> 
> This adds a feature bit for asymmetric packing to powerpc and then
> enables it on POWER7. 
> 
> Signed-off-by: Michael Neuling <mikey@neuling.org>

Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

> 
> ---
> 
>  arch/powerpc/include/asm/cputable.h |    3 ++-
>  arch/powerpc/kernel/process.c       |    9 +++++++++
>  2 files changed, 11 insertions(+), 1 deletion(-)
> 
> Index: linux-2.6-ozlabs/arch/powerpc/include/asm/cputable.h
> ===================================================================
> --- linux-2.6-ozlabs.orig/arch/powerpc/include/asm/cputable.h
> +++ linux-2.6-ozlabs/arch/powerpc/include/asm/cputable.h
> @@ -195,6 +195,7 @@ extern const char *powerpc_base_platform
>  #define CPU_FTR_SAO			LONG_ASM_CONST(0x0020000000000000)
>  #define CPU_FTR_CP_USE_DCBTZ		LONG_ASM_CONST(0x0040000000000000)
>  #define CPU_FTR_UNALIGNED_LD_STD	LONG_ASM_CONST(0x0080000000000000)
> +#define CPU_FTR_ASYM_SMT		LONG_ASM_CONST(0x0100000000000000)
>  
>  #ifndef __ASSEMBLY__
>  
> @@ -409,7 +410,7 @@ extern const char *powerpc_base_platform
>  	    CPU_FTR_MMCRA | CPU_FTR_SMT | \
>  	    CPU_FTR_COHERENT_ICACHE | CPU_FTR_LOCKLESS_TLBIE | \
>  	    CPU_FTR_PURR | CPU_FTR_SPURR | CPU_FTR_REAL_LE | \
> -	    CPU_FTR_DSCR | CPU_FTR_SAO)
> +	    CPU_FTR_DSCR | CPU_FTR_SAO  | CPU_FTR_ASYM_SMT)
>  #define CPU_FTRS_CELL	(CPU_FTR_USE_TB | CPU_FTR_LWSYNC | \
>  	    CPU_FTR_PPCAS_ARCH_V2 | CPU_FTR_CTRL | \
>  	    CPU_FTR_ALTIVEC_COMP | CPU_FTR_MMCRA | CPU_FTR_SMT | \
> Index: linux-2.6-ozlabs/arch/powerpc/kernel/process.c
> ===================================================================
> --- linux-2.6-ozlabs.orig/arch/powerpc/kernel/process.c
> +++ linux-2.6-ozlabs/arch/powerpc/kernel/process.c
> @@ -1265,3 +1265,12 @@ unsigned long randomize_et_dyn(unsigned 
>  
>  	return ret;
>  }
> +
> +int arch_sd_sibiling_asym_packing(void)
> +{
> +	if (cpu_has_feature(CPU_FTR_ASYM_SMT)){
> +		printk_once(KERN_INFO "Enabling Asymmetric SMT scheduling\n");
> +		return SD_ASYM_PACKING;
> +	}
> +	return 0;
> +}

[tip:sched/core] powerpc: Enable asymmetric SMT scheduling on POWER7

[tip-bot for Michael Neuling]

Commit-ID:  76cbd8a8f8b0dddbff89a6708bd5bd13c0d21a00
Gitweb:     http://git.kernel.org/tip/76cbd8a8f8b0dddbff89a6708bd5bd13c0d21a00
Author:     Michael Neuling <mikey@neuling.org>
AuthorDate: Tue, 8 Jun 2010 14:57:02 +1000
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Wed, 9 Jun 2010 11:13:14 +0200

powerpc: Enable asymmetric SMT scheduling on POWER7

The POWER7 core has dynamic SMT mode switching which is controlled by
the hypervisor.  There are 3 SMT modes:
	SMT1 uses thread  0
	SMT2 uses threads 0 & 1
	SMT4 uses threads 0, 1, 2 & 3
When in any particular SMT mode, all threads have the same performance
as each other (ie. at any moment in time, all threads perform the same).

The SMT mode switching works such that when linux has threads 2 & 3 idle
and 0 & 1 active, it will cede (H_CEDE hypercall) threads 2 and 3 in the
idle loop and the hypervisor will automatically switch to SMT2 for that
core (independent of other cores).  The opposite is not true, so if
threads 0 & 1 are idle and 2 & 3 are active, we will stay in SMT4 mode.

Similarly if thread 0 is active and threads 1, 2 & 3 are idle, we'll go
into SMT1 mode.

If we can get the core into a lower SMT mode (SMT1 is best), the threads
will perform better (since they share less core resources).  Hence when
we have idle threads, we want them to be the higher ones.

This adds a feature bit for asymmetric packing to powerpc and then
enables it on POWER7.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: linuxppc-dev@ozlabs.org
LKML-Reference: <20100608045702.31FB5CC8C7@localhost.localdomain>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 arch/powerpc/include/asm/cputable.h |    3 ++-
 arch/powerpc/kernel/process.c       |    9 +++++++++
 2 files changed, 11 insertions(+), 1 deletions(-)

diff --git a/arch/powerpc/include/asm/cputable.h b/arch/powerpc/include/asm/cputable.h
index b0b2113..4b611ca 100644
--- a/arch/powerpc/include/asm/cputable.h
+++ b/arch/powerpc/include/asm/cputable.h
@@ -197,6 +197,7 @@ extern const char *powerpc_base_platform;
 #define CPU_FTR_SAO			LONG_ASM_CONST(0x0020000000000000)
 #define CPU_FTR_CP_USE_DCBTZ		LONG_ASM_CONST(0x0040000000000000)
 #define CPU_FTR_UNALIGNED_LD_STD	LONG_ASM_CONST(0x0080000000000000)
+#define CPU_FTR_ASYM_SMT		LONG_ASM_CONST(0x0100000000000000)
 
 #ifndef __ASSEMBLY__
 
@@ -412,7 +413,7 @@ extern const char *powerpc_base_platform;
 	    CPU_FTR_MMCRA | CPU_FTR_SMT | \
 	    CPU_FTR_COHERENT_ICACHE | CPU_FTR_LOCKLESS_TLBIE | \
 	    CPU_FTR_PURR | CPU_FTR_SPURR | CPU_FTR_REAL_LE | \
-	    CPU_FTR_DSCR | CPU_FTR_SAO)
+	    CPU_FTR_DSCR | CPU_FTR_SAO  | CPU_FTR_ASYM_SMT)
 #define CPU_FTRS_CELL	(CPU_FTR_USE_TB | CPU_FTR_LWSYNC | \
 	    CPU_FTR_PPCAS_ARCH_V2 | CPU_FTR_CTRL | \
 	    CPU_FTR_ALTIVEC_COMP | CPU_FTR_MMCRA | CPU_FTR_SMT | \
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 9d255b4..a3f347c 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1268,3 +1268,12 @@ unsigned long randomize_et_dyn(unsigned long base)
 
 	return ret;
 }
+
+int arch_sd_sibiling_asym_packing(void)
+{
+	if (cpu_has_feature(CPU_FTR_ASYM_SMT)) {
+		printk_once(KERN_INFO "Enabling Asymmetric SMT scheduling\n");
+		return SD_ASYM_PACKING;
+	}
+	return 0;
+}

[tip:sched/core] powerpc: Exclude arch_sd_sibiling_asym_packing() on UP

[tip-bot for Peter Zijlstra]

Commit-ID:  00318f5eea0642c29212bff76ba500f620400d78
Gitweb:     http://git.kernel.org/tip/00318f5eea0642c29212bff76ba500f620400d78
Author:     Peter Zijlstra <a.p.zijlstra@chello.nl>
AuthorDate: Wed, 9 Jun 2010 16:20:55 +0200
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Wed, 9 Jun 2010 16:24:36 +0200

powerpc: Exclude arch_sd_sibiling_asym_packing() on UP

Only SMP systems care about load-balance features, plus this
saves some .text space on UP and also fixes the build.

Reported-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <tip-76cbd8a8f8b0dddbff89a6708bd5bd13c0d21a00@git.kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 arch/powerpc/kernel/process.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index a3f347c..9b41ece 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1269,6 +1269,7 @@ unsigned long randomize_et_dyn(unsigned long base)
 	return ret;
 }
 
+#ifdef CONFIG_SMP
 int arch_sd_sibiling_asym_packing(void)
 {
 	if (cpu_has_feature(CPU_FTR_ASYM_SMT)) {
@@ -1277,3 +1278,4 @@ int arch_sd_sibiling_asym_packing(void)
 	}
 	return 0;
 }
+#endif

[tip:sched/core] powerpc: Exclude arch_sd_sibiling_asym_packing() on UP

[tip-bot for Peter Zijlstra]

Commit-ID:  89275d59b572b92b1e2f6ddb63c49deecb801ff9
Gitweb:     http://git.kernel.org/tip/89275d59b572b92b1e2f6ddb63c49deecb801ff9
Author:     Peter Zijlstra <a.p.zijlstra@chello.nl>
AuthorDate: Wed, 9 Jun 2010 16:20:55 +0200
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Wed, 9 Jun 2010 16:31:39 +0200

powerpc: Exclude arch_sd_sibiling_asym_packing() on UP

Only SMP systems care about load-balance features, plus this
saves some .text space on UP and also fixes the build.

Reported-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Michael Neuling <mikey@neuling.org>
LKML-Reference: <tip-76cbd8a8f8b0dddbff89a6708bd5bd13c0d21a00@git.kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 arch/powerpc/kernel/process.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index a3f347c..9b41ece 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1269,6 +1269,7 @@ unsigned long randomize_et_dyn(unsigned long base)
 	return ret;
 }
 
+#ifdef CONFIG_SMP
 int arch_sd_sibiling_asym_packing(void)
 {
 	if (cpu_has_feature(CPU_FTR_ASYM_SMT)) {
@@ -1277,3 +1278,4 @@ int arch_sd_sibiling_asym_packing(void)
 	}
 	return 0;
 }
+#endif

[PATCH 1/3] sched: fix capacity calculations for SMT4

[Michael Neuling]

From: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>

Handle cpu capacity being reported as 0 on cores with more number of
hardware threads. For example on a Power7 core with 4 hardware
threads, core power is 1177 and thus power of each hardware thread is
1177/4 = 294. This low power can lead to capacity for each hardware
thread being calculated as 0, which leads to tasks bouncing within the
core madly! 

Fix this by reporting capacity for hardware threads as 1, provided
their power is not scaled down significantly because of frequency
scaling or real-time tasks usage of cpu.

Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Michael Neuling <mikey@neuling.org>

---

 include/linux/sched.h |    2 -
 kernel/sched_fair.c   |   56 +++++++++++++++++++++++++++++++++++++++++---------
 2 files changed, 48 insertions(+), 10 deletions(-)

Index: linux-2.6/include/linux/sched.h
===================================================================
--- linux-2.6.orig/include/linux/sched.h
+++ linux-2.6/include/linux/sched.h
@@ -860,7 +860,7 @@ struct sched_group {
 	 * CPU power of this group, SCHED_LOAD_SCALE being max power for a
 	 * single CPU.
 	 */
-	unsigned int cpu_power;
+	unsigned int cpu_power, cpu_power_orig;
 
 	/*
 	 * The CPUs this group covers.
Index: linux-2.6/kernel/sched_fair.c
===================================================================
--- linux-2.6.orig/kernel/sched_fair.c
+++ linux-2.6/kernel/sched_fair.c
@@ -2285,13 +2285,6 @@ static void update_cpu_power(struct sche
 	unsigned long power = SCHED_LOAD_SCALE;
 	struct sched_group *sdg = sd->groups;
 
-	if (sched_feat(ARCH_POWER))
-		power *= arch_scale_freq_power(sd, cpu);
-	else
-		power *= default_scale_freq_power(sd, cpu);
-
-	power >>= SCHED_LOAD_SHIFT;
-
 	if ((sd->flags & SD_SHARE_CPUPOWER) && weight > 1) {
 		if (sched_feat(ARCH_POWER))
 			power *= arch_scale_smt_power(sd, cpu);
@@ -2301,6 +2294,15 @@ static void update_cpu_power(struct sche
 		power >>= SCHED_LOAD_SHIFT;
 	}
 
+	sdg->cpu_power_orig = power;
+
+	if (sched_feat(ARCH_POWER))
+		power *= arch_scale_freq_power(sd, cpu);
+	else
+		power *= default_scale_freq_power(sd, cpu);
+
+	power >>= SCHED_LOAD_SHIFT;
+
 	power *= scale_rt_power(cpu);
 	power >>= SCHED_LOAD_SHIFT;
 
@@ -2333,6 +2335,36 @@ static void update_group_power(struct sc
 	sdg->cpu_power = power;
 }
 
+/*
+ * What's the influence of freq. scaling or real-time tasks on a cpu's power?
+ *
+ * Return 1 (influence exists) if power was scaled by more than 10% due to
+ * either factor, else return 0 (i.e no influence exists).
+ *
+ * This is specifically needed to handle capacity being reported as 0 for
+ * hardware threads within a Power7-like core (that have 4 or more hardware
+ * threads/core).
+ */
+static inline int
+rt_freq_influence(struct sched_group *group, struct sched_domain *sd)
+{
+	/* We need this test only at SMT domain level */
+	if (sd->child)
+		return 1;
+
+	/*
+	 * Check to see if the final cpu power was reduced by more than 10% due
+	 * to frequency scaling or real-time task's cpu usage. Note that
+	 * cpu_power could be different from cpu_power_orig even in the absence
+	 * of either factors - this is due to rounding issues in
+	 * update_cpu_power()
+	 */
+	if (group->cpu_power * 100 < group->cpu_power_orig * 90)
+		return 1;
+
+	return 0;
+}
+
 /**
  * update_sg_lb_stats - Update sched_group's statistics for load balancing.
  * @sd: The sched_domain whose statistics are to be updated.
@@ -2426,6 +2458,8 @@ static inline void update_sg_lb_stats(st
 
 	sgs->group_capacity =
 		DIV_ROUND_CLOSEST(group->cpu_power, SCHED_LOAD_SCALE);
+	if (!sgs->group_capacity && !rt_freq_influence(group, sd))
+		sgs->group_capacity = 1;
 }
 
 /**
@@ -2725,7 +2759,8 @@ ret:
  */
 static struct rq *
 find_busiest_queue(struct sched_group *group, enum cpu_idle_type idle,
-		   unsigned long imbalance, const struct cpumask *cpus)
+		   unsigned long imbalance, const struct cpumask *cpus,
+		   struct sched_domain *sd)
 {
 	struct rq *busiest = NULL, *rq;
 	unsigned long max_load = 0;
@@ -2736,6 +2771,9 @@ find_busiest_queue(struct sched_group *g
 		unsigned long capacity = DIV_ROUND_CLOSEST(power, SCHED_LOAD_SCALE);
 		unsigned long wl;
 
+		if (!capacity && !rt_freq_influence(group, sd))
+			capacity = 1;
+
 		if (!cpumask_test_cpu(i, cpus))
 			continue;
 
@@ -2852,7 +2890,7 @@ redo:
 		goto out_balanced;
 	}
 
-	busiest = find_busiest_queue(group, idle, imbalance, cpus);
+	busiest = find_busiest_queue(group, idle, imbalance, cpus, sd);
 	if (!busiest) {
 		schedstat_inc(sd, lb_nobusyq[idle]);
 		goto out_balanced;

[tip:sched/core] sched: Fix capacity calculations for SMT4

[tip-bot for Srivatsa Vaddagiri]

Commit-ID:  9d5efe05eb0c904545a28b19c18b949f23334de0
Gitweb:     http://git.kernel.org/tip/9d5efe05eb0c904545a28b19c18b949f23334de0
Author:     Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
AuthorDate: Tue, 8 Jun 2010 14:57:02 +1000
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Wed, 9 Jun 2010 10:34:54 +0200

sched: Fix capacity calculations for SMT4

Handle cpu capacity being reported as 0 on cores with more number of
hardware threads. For example on a Power7 core with 4 hardware
threads, core power is 1177 and thus power of each hardware thread is
1177/4 = 294. This low power can lead to capacity for each hardware
thread being calculated as 0, which leads to tasks bouncing within the
core madly!

Fix this by reporting capacity for hardware threads as 1, provided
their power is not scaled down significantly because of frequency
scaling or real-time tasks usage of cpu.

Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arjan van de Ven <arjan@linux.intel.com>
LKML-Reference: <20100608045702.21D03CC895@localhost.localdomain>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 include/linux/sched.h |    2 +-
 kernel/sched_fair.c   |   53 +++++++++++++++++++++++++++++++++++++++---------
 2 files changed, 44 insertions(+), 11 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index a3e5b1c..c731296 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -857,7 +857,7 @@ struct sched_group {
 	 * CPU power of this group, SCHED_LOAD_SCALE being max power for a
 	 * single CPU.
 	 */
-	unsigned int cpu_power;
+	unsigned int cpu_power, cpu_power_orig;
 
 	/*
 	 * The CPUs this group covers.
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 6ee2e0a..b9b3462 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -2285,13 +2285,6 @@ static void update_cpu_power(struct sched_domain *sd, int cpu)
 	unsigned long power = SCHED_LOAD_SCALE;
 	struct sched_group *sdg = sd->groups;
 
-	if (sched_feat(ARCH_POWER))
-		power *= arch_scale_freq_power(sd, cpu);
-	else
-		power *= default_scale_freq_power(sd, cpu);
-
-	power >>= SCHED_LOAD_SHIFT;
-
 	if ((sd->flags & SD_SHARE_CPUPOWER) && weight > 1) {
 		if (sched_feat(ARCH_POWER))
 			power *= arch_scale_smt_power(sd, cpu);
@@ -2301,6 +2294,15 @@ static void update_cpu_power(struct sched_domain *sd, int cpu)
 		power >>= SCHED_LOAD_SHIFT;
 	}
 
+	sdg->cpu_power_orig = power;
+
+	if (sched_feat(ARCH_POWER))
+		power *= arch_scale_freq_power(sd, cpu);
+	else
+		power *= default_scale_freq_power(sd, cpu);
+
+	power >>= SCHED_LOAD_SHIFT;
+
 	power *= scale_rt_power(cpu);
 	power >>= SCHED_LOAD_SHIFT;
 
@@ -2333,6 +2335,31 @@ static void update_group_power(struct sched_domain *sd, int cpu)
 	sdg->cpu_power = power;
 }
 
+/*
+ * Try and fix up capacity for tiny siblings, this is needed when
+ * things like SD_ASYM_PACKING need f_b_g to select another sibling
+ * which on its own isn't powerful enough.
+ *
+ * See update_sd_pick_busiest() and check_asym_packing().
+ */
+static inline int
+fix_small_capacity(struct sched_domain *sd, struct sched_group *group)
+{
+	/*
+	 * Only siblings can have significantly less than SCHED_LOAD_SCALE
+	 */
+	if (sd->level != SD_LV_SIBLING)
+		return 0;
+
+	/*
+	 * If ~90% of the cpu_power is still there, we're good.
+	 */
+	if (group->cpu_power * 32 < group->cpu_power_orig * 29)
+		return 1;
+
+	return 0;
+}
+
 /**
  * update_sg_lb_stats - Update sched_group's statistics for load balancing.
  * @sd: The sched_domain whose statistics are to be updated.
@@ -2426,6 +2453,8 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
 
 	sgs->group_capacity =
 		DIV_ROUND_CLOSEST(group->cpu_power, SCHED_LOAD_SCALE);
+	if (!sgs->group_capacity)
+		sgs->group_capacity = fix_small_capacity(sd, group);
 }
 
 /**
@@ -2724,8 +2753,9 @@ ret:
  * find_busiest_queue - find the busiest runqueue among the cpus in group.
  */
 static struct rq *
-find_busiest_queue(struct sched_group *group, enum cpu_idle_type idle,
-		   unsigned long imbalance, const struct cpumask *cpus)
+find_busiest_queue(struct sched_domain *sd, struct sched_group *group,
+		   enum cpu_idle_type idle, unsigned long imbalance,
+		   const struct cpumask *cpus)
 {
 	struct rq *busiest = NULL, *rq;
 	unsigned long max_load = 0;
@@ -2736,6 +2766,9 @@ find_busiest_queue(struct sched_group *group, enum cpu_idle_type idle,
 		unsigned long capacity = DIV_ROUND_CLOSEST(power, SCHED_LOAD_SCALE);
 		unsigned long wl;
 
+		if (!capacity)
+			capacity = fix_small_capacity(sd, group);
+
 		if (!cpumask_test_cpu(i, cpus))
 			continue;
 
@@ -2852,7 +2885,7 @@ redo:
 		goto out_balanced;
 	}
 
-	busiest = find_busiest_queue(group, idle, imbalance, cpus);
+	busiest = find_busiest_queue(sd, group, idle, imbalance, cpus);
 	if (!busiest) {
 		schedstat_inc(sd, lb_nobusyq[idle]);
 		goto out_balanced;

Re: [tip:sched/core] sched: Fix capacity calculations for SMT4

[Michael Neuling]

Peter,

It looks like when this was pushed to Ingo, some of the logic was
changed.  rt_freq_influence() became fix_small_capacity() but the return
values for these two functions are opposite (return 1 => return 0 and
visa versa]]).

This was changed in the sibling test (return 1 => return 0), but the
check for the change in cpu power due to freq and rt was not.

So either the return values need to be changed at the end of
fix_small_capacity() or the cpu_power test needs to be the other way
around.  Below changes the cpu_power test as it brings it more inline
with the comment above it.

Without this the asymmetric packing doesn't work.

Mikey
---
Subject: sched: fix the CPU power test for fix_small_capacity

The CPU power test is the wrong way around in fix_small_capacity.

This was due to a small changes made in the posted patch on lkml to what
was was taken upstream.

This patch fixes asymmetric packing for POWER7.

Signed-off-by: Michael Neuling <mikey@neuling.org>

Index: linux-2.6-ozlabs/kernel/sched_fair.c
===================================================================
--- linux-2.6-ozlabs.orig/kernel/sched_fair.c
+++ linux-2.6-ozlabs/kernel/sched_fair.c
@@ -2354,7 +2354,7 @@ fix_small_capacity(struct sched_domain *
 	/*
 	 * If ~90% of the cpu_power is still there, we're good.
 	 */
-	if (group->cpu_power * 32 < group->cpu_power_orig * 29)
+	if (group->cpu_power * 32 > group->cpu_power_orig * 29)
 		return 1;
 
 	return 0;


In message <tip-9d5efe05eb0c904545a28b19c18b949f23334de0@git.kernel.org> you wr
ote:
> Commit-ID:  9d5efe05eb0c904545a28b19c18b949f23334de0
> Gitweb:     http://git.kernel.org/tip/9d5efe05eb0c904545a28b19c18b949f23334de
0
> Author:     Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
> AuthorDate: Tue, 8 Jun 2010 14:57:02 +1000
> Committer:  Ingo Molnar <mingo@elte.hu>
> CommitDate: Wed, 9 Jun 2010 10:34:54 +0200
> 
> sched: Fix capacity calculations for SMT4
> 
> Handle cpu capacity being reported as 0 on cores with more number of
> hardware threads. For example on a Power7 core with 4 hardware
> threads, core power is 1177 and thus power of each hardware thread is
> 1177/4 = 294. This low power can lead to capacity for each hardware
> thread being calculated as 0, which leads to tasks bouncing within the
> core madly!
> 
> Fix this by reporting capacity for hardware threads as 1, provided
> their power is not scaled down significantly because of frequency
> scaling or real-time tasks usage of cpu.
> 
> Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
> Signed-off-by: Michael Neuling <mikey@neuling.org>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Cc: Arjan van de Ven <arjan@linux.intel.com>
> LKML-Reference: <20100608045702.21D03CC895@localhost.localdomain>
> Signed-off-by: Ingo Molnar <mingo@elte.hu>
> ---
>  include/linux/sched.h |    2 +-
>  kernel/sched_fair.c   |   53 +++++++++++++++++++++++++++++++++++++++--------
-
>  2 files changed, 44 insertions(+), 11 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index a3e5b1c..c731296 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -857,7 +857,7 @@ struct sched_group {
>  	 * CPU power of this group, SCHED_LOAD_SCALE being max power for a
>  	 * single CPU.
>  	 */
> -	unsigned int cpu_power;
> +	unsigned int cpu_power, cpu_power_orig;
>  
>  	/*
>  	 * The CPUs this group covers.
> diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
> index 6ee2e0a..b9b3462 100644
> --- a/kernel/sched_fair.c
> +++ b/kernel/sched_fair.c
> @@ -2285,13 +2285,6 @@ static void update_cpu_power(struct sched_domain *sd, 
int cpu)
>  	unsigned long power = SCHED_LOAD_SCALE;
>  	struct sched_group *sdg = sd->groups;
>  
> -	if (sched_feat(ARCH_POWER))
> -		power *= arch_scale_freq_power(sd, cpu);
> -	else
> -		power *= default_scale_freq_power(sd, cpu);
> -
> -	power >>= SCHED_LOAD_SHIFT;
> -
>  	if ((sd->flags & SD_SHARE_CPUPOWER) && weight > 1) {
>  		if (sched_feat(ARCH_POWER))
>  			power *= arch_scale_smt_power(sd, cpu);
> @@ -2301,6 +2294,15 @@ static void update_cpu_power(struct sched_domain *sd, 
int cpu)
>  		power >>= SCHED_LOAD_SHIFT;
>  	}
>  
> +	sdg->cpu_power_orig = power;
> +
> +	if (sched_feat(ARCH_POWER))
> +		power *= arch_scale_freq_power(sd, cpu);
> +	else
> +		power *= default_scale_freq_power(sd, cpu);
> +
> +	power >>= SCHED_LOAD_SHIFT;
> +
>  	power *= scale_rt_power(cpu);
>  	power >>= SCHED_LOAD_SHIFT;
>  
> @@ -2333,6 +2335,31 @@ static void update_group_power(struct sched_domain *sd
, int cpu)
>  	sdg->cpu_power = power;
>  }
>  
> +/*
> + * Try and fix up capacity for tiny siblings, this is needed when
> + * things like SD_ASYM_PACKING need f_b_g to select another sibling
> + * which on its own isn't powerful enough.
> + *
> + * See update_sd_pick_busiest() and check_asym_packing().
> + */
> +static inline int
> +fix_small_capacity(struct sched_domain *sd, struct sched_group *group)
> +{
> +	/*
> +	 * Only siblings can have significantly less than SCHED_LOAD_SCALE
> +	 */
> +	if (sd->level != SD_LV_SIBLING)
> +		return 0;
> +
> +	/*
> +	 * If ~90% of the cpu_power is still there, we're good.
> +	 */
> +	if (group->cpu_power * 32 < group->cpu_power_orig * 29)
> +		return 1;
> +
> +	return 0;
> +}
> +
>  /**
>   * update_sg_lb_stats - Update sched_group's statistics for load balancing.
>   * @sd: The sched_domain whose statistics are to be updated.
> @@ -2426,6 +2453,8 @@ static inline void update_sg_lb_stats(struct sched_doma
in *sd,
>  
>  	sgs->group_capacity =
>  		DIV_ROUND_CLOSEST(group->cpu_power, SCHED_LOAD_SCALE);
> +	if (!sgs->group_capacity)
> +		sgs->group_capacity = fix_small_capacity(sd, group);
>  }
>  
>  /**
> @@ -2724,8 +2753,9 @@ ret:
>   * find_busiest_queue - find the busiest runqueue among the cpus in group.
>   */
>  static struct rq *
> -find_busiest_queue(struct sched_group *group, enum cpu_idle_type idle,
> -		   unsigned long imbalance, const struct cpumask *cpus)
> +find_busiest_queue(struct sched_domain *sd, struct sched_group *group,
> +		   enum cpu_idle_type idle, unsigned long imbalance,
> +		   const struct cpumask *cpus)
>  {
>  	struct rq *busiest = NULL, *rq;
>  	unsigned long max_load = 0;
> @@ -2736,6 +2766,9 @@ find_busiest_queue(struct sched_group *group, enum cpu_
idle_type idle,
>  		unsigned long capacity = DIV_ROUND_CLOSEST(power, SCHED_LOAD_SC
ALE);
>  		unsigned long wl;
>  
> +		if (!capacity)
> +			capacity = fix_small_capacity(sd, group);
> +
>  		if (!cpumask_test_cpu(i, cpus))
>  			continue;
>  
> @@ -2852,7 +2885,7 @@ redo:
>  		goto out_balanced;
>  	}
>  
> -	busiest = find_busiest_queue(group, idle, imbalance, cpus);
> +	busiest = find_busiest_queue(sd, group, idle, imbalance, cpus);
>  	if (!busiest) {
>  		schedstat_inc(sd, lb_nobusyq[idle]);
>  		goto out_balanced;
> 

[PATCH] sched: update comments to make docbook happy

[Michael Neuling]

Docbook fails in sched_fair.c due to comments added in the asymmetric
packing patch series.

This fixes these errors.  No code changes.

Signed-off-by: Michael Neuling <mikey@neuling.org>
---

Index: linux-2.6-ozlabs/kernel/sched_fair.c
===================================================================
--- linux-2.6-ozlabs.orig/kernel/sched_fair.c
+++ linux-2.6-ozlabs/kernel/sched_fair.c
@@ -2462,7 +2462,8 @@ static inline void update_sg_lb_stats(st
  * @sd: sched_domain whose statistics are to be checked
  * @sds: sched_domain statistics
  * @sg: sched_group candidate to be checked for being the busiest
- * @sds: sched_group statistics
+ * @sgs: sched_group statistics
+ * @this_cpu: the current cpu
  *
  * Determine if @sg is a busier group than the previously selected
  * busiest group.
@@ -2588,13 +2589,13 @@ int __weak arch_sd_sibiling_asym_packing
  * assuming lower CPU number will be equivalent to lower a SMT thread
  * number.
  *
+ * Returns 1 when packing is required and a task should be moved to
+ * this CPU.  The amount of the imbalance is returned in *imbalance.
+ *
  * @sd: The sched_domain whose packing is to be checked.
  * @sds: Statistics of the sched_domain which is to be packed
  * @this_cpu: The cpu at whose sched_domain we're performing load-balance.
  * @imbalance: returns amount of imbalanced due to packing.
- *
- * Returns 1 when packing is required and a task should be moved to
- * this CPU.  The amount of the imbalance is returned in *imbalance.
  */
 static int check_asym_packing(struct sched_domain *sd,
 			      struct sd_lb_stats *sds,

[tip:sched/core] sched: Fix comments to make them DocBook happy

[tip-bot for Michael Neuling]

Commit-ID:  b6b12294405e6ec029e627c49adf3193829a2685
Gitweb:     http://git.kernel.org/tip/b6b12294405e6ec029e627c49adf3193829a2685
Author:     Michael Neuling <mikey@neuling.org>
AuthorDate: Thu, 10 Jun 2010 12:06:21 +1000
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Fri, 18 Jun 2010 10:46:55 +0200

sched: Fix comments to make them DocBook happy

Docbook fails in sched_fair.c due to comments added in the asymmetric
packing patch series.

This fixes these errors. No code changes.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <24737.1276135581@neuling.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 kernel/sched_fair.c |    9 +++++----
 1 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index e82c572..5e8f98c 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -2462,7 +2462,8 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
  * @sd: sched_domain whose statistics are to be checked
  * @sds: sched_domain statistics
  * @sg: sched_group candidate to be checked for being the busiest
- * @sds: sched_group statistics
+ * @sgs: sched_group statistics
+ * @this_cpu: the current cpu
  *
  * Determine if @sg is a busier group than the previously selected
  * busiest group.
@@ -2588,13 +2589,13 @@ int __weak arch_sd_sibiling_asym_packing(void)
  * assuming lower CPU number will be equivalent to lower a SMT thread
  * number.
  *
+ * Returns 1 when packing is required and a task should be moved to
+ * this CPU.  The amount of the imbalance is returned in *imbalance.
+ *
  * @sd: The sched_domain whose packing is to be checked.
  * @sds: Statistics of the sched_domain which is to be packed
  * @this_cpu: The cpu at whose sched_domain we're performing load-balance.
  * @imbalance: returns amount of imbalanced due to packing.
- *
- * Returns 1 when packing is required and a task should be moved to
- * this CPU.  The amount of the imbalance is returned in *imbalance.
  */
 static int check_asym_packing(struct sched_domain *sd,
 			      struct sd_lb_stats *sds,

Re: [tip:sched/core] sched: Fix capacity calculations for SMT4

[Peter Zijlstra]

On Thu, 2010-06-10 at 09:03 +1000, Michael Neuling wrote:
> Peter,
> 
> It looks like when this was pushed to Ingo, some of the logic was
> changed.  rt_freq_influence() became fix_small_capacity() but the return
> values for these two functions are opposite (return 1 => return 0 and
> visa versa]]).
> 
> This was changed in the sibling test (return 1 => return 0), but the
> check for the change in cpu power due to freq and rt was not.
> 
> So either the return values need to be changed at the end of
> fix_small_capacity() or the cpu_power test needs to be the other way
> around.  Below changes the cpu_power test as it brings it more inline
> with the comment above it.
> 
> Without this the asymmetric packing doesn't work.

D'oh fully my fault for cleaning up.

Thanks, I'll make sure it gets fixed.

> Subject: sched: fix the CPU power test for fix_small_capacity
> 
> The CPU power test is the wrong way around in fix_small_capacity.
> 
> This was due to a small changes made in the posted patch on lkml to what
> was was taken upstream.
> 
> This patch fixes asymmetric packing for POWER7.
> 
> Signed-off-by: Michael Neuling <mikey@neuling.org>
> 
> Index: linux-2.6-ozlabs/kernel/sched_fair.c
> ===================================================================
> --- linux-2.6-ozlabs.orig/kernel/sched_fair.c
> +++ linux-2.6-ozlabs/kernel/sched_fair.c
> @@ -2354,7 +2354,7 @@ fix_small_capacity(struct sched_domain *
>  	/*
>  	 * If ~90% of the cpu_power is still there, we're good.
>  	 */
> -	if (group->cpu_power * 32 < group->cpu_power_orig * 29)
> +	if (group->cpu_power * 32 > group->cpu_power_orig * 29)
>  		return 1;
>  
>  	return 0;
> 

Re: [tip:sched/core] sched: Fix capacity calculations for SMT4

[Michael Neuling]

In message <1276152536.2046.2479.camel@twins> you wrote:
> On Thu, 2010-06-10 at 09:03 +1000, Michael Neuling wrote:
> > Peter,
> >=20
> > It looks like when this was pushed to Ingo, some of the logic was
> > changed.  rt_freq_influence() became fix_small_capacity() but the return
> > values for these two functions are opposite (return 1 =3D> return 0 and
> > visa versa]]).
> >=20
> > This was changed in the sibling test (return 1 =3D> return 0), but the
> > check for the change in cpu power due to freq and rt was not.
> >=20
> > So either the return values need to be changed at the end of
> > fix_small_capacity() or the cpu_power test needs to be the other way
> > around.  Below changes the cpu_power test as it brings it more inline
> > with the comment above it.
> >=20
> > Without this the asymmetric packing doesn't work.
> 
> D'oh fully my fault for cleaning up.
> 
> Thanks, I'll make sure it gets fixed.

Peter,

I've not see this fix (or the doc/comment update patch from here
https://patchwork.kernel.org/patch/105256/) hit Ingo tip tree as yet.
When you are likely to push it to him?

Mikey

> 
> > Subject: sched: fix the CPU power test for fix_small_capacity
> >=20
> > The CPU power test is the wrong way around in fix_small_capacity.
> >=20
> > This was due to a small changes made in the posted patch on lkml to what
> > was was taken upstream.
> >=20
> > This patch fixes asymmetric packing for POWER7.
> >=20
> > Signed-off-by: Michael Neuling <mikey@neuling.org>
> >=20
> > Index: linux-2.6-ozlabs/kernel/sched_fair.c
> > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> > --- linux-2.6-ozlabs.orig/kernel/sched_fair.c
> > +++ linux-2.6-ozlabs/kernel/sched_fair.c
> > @@ -2354,7 +2354,7 @@ fix_small_capacity(struct sched_domain *
> >  	/*
> >  	 * If ~90% of the cpu_power is still there, we're good.
> >  	 */
> > -	if (group->cpu_power * 32 < group->cpu_power_orig * 29)
> > +	if (group->cpu_power * 32 > group->cpu_power_orig * 29)
> >  		return 1;
> > =20
> >  	return 0;
> >=20
> 

[tip:sched/core] sched: Fix fix_small_capacity

[tip-bot for Michael Neuling]

Commit-ID:  694f5a1112959a6996cabdb6f8d3003e87dac8a7
Gitweb:     http://git.kernel.org/tip/694f5a1112959a6996cabdb6f8d3003e87dac8a7
Author:     Michael Neuling <mikey@neuling.org>
AuthorDate: Thu, 10 Jun 2010 09:03:37 +1000
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Fri, 18 Jun 2010 10:46:54 +0200

sched: Fix fix_small_capacity

The CPU power test is the wrong way around in fix_small_capacity.

This was due to a small changes made in the posted patch on lkml to what
was was taken upstream.

This patch fixes asymmetric packing for POWER7.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <12629.1276124617@neuling.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 kernel/sched_fair.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 593424f..e82c572 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -2354,7 +2354,7 @@ fix_small_capacity(struct sched_domain *sd, struct sched_group *group)
 	/*
 	 * If ~90% of the cpu_power is still there, we're good.
 	 */
-	if (group->cpu_power * 32 < group->cpu_power_orig * 29)
+	if (group->cpu_power * 32 > group->cpu_power_orig * 29)
 		return 1;
 
 	return 0;