sched: Remove stale power aware scheduling remnants and dysfunctional knobs

Peter Zijlstra · Ingo Molnar · commit 8e7fbcbc22c1 · 2012-05-17T13:48:56.000+02:00
It's been broken forever (i.e. it's not scheduling in a power aware fashion), as reported by Suresh and others sending patches, and nobody cares enough to fix it properly ... so remove it to make space free for something better. There's various problems with the code as it stands today, first and foremost the user interface which is bound to topology levels and has multiple values per level. This results in a state explosion which the administrator or distro needs to master and almost nobody does. Furthermore large configuration state spaces aren't good, it means the thing doesn't just work right because it's either under so many impossibe to meet constraints, or even if there's an achievable state workloads have to be aware of it precisely and can never meet it for dynamic workloads. So pushing this kind of decision to user-space was a bad idea even with a single knob - it's exponentially worse with knobs on every node of the topology. There is a proposal to replace the user interface with a single 3 state knob: sched_balance_policy := { performance, power, auto } where 'auto' would be the preferred default which looks at things like Battery/AC mode and possible cpufreq state or whatever the hw exposes to show us power use expectations - but there's been no progress on it in the past many months. Aside from that, the actual implementation of the various knobs is known to be broken. There have been sporadic attempts at fixing things but these always stop short of reaching a mergable state. Therefore this wholesale removal with the hopes of spurring people who care to come forward once again and work on a coherent replacement. Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Suresh Siddha <suresh.b.siddha@intel.com> Cc: Arjan van de Ven <arjan@linux.intel.com> Cc: Vincent Guittot <vincent.guittot@linaro.org> Cc: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Link: http://lkml.kernel.org/r/1326104915.2442.53.camel@twins Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
@@ -9,31 +9,6 @@ Description:
 
 		/sys/devices/system/cpu/cpu#/
 
-What:		/sys/devices/system/cpu/sched_mc_power_savings
-		/sys/devices/system/cpu/sched_smt_power_savings
-Date:		June 2006
-Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>
-Description:	Discover and adjust the kernel's multi-core scheduler support.
-
-		Possible values are:
-
-		0 - No power saving load balance (default value)
-		1 - Fill one thread/core/package first for long running threads
-		2 - Also bias task wakeups to semi-idle cpu package for power
-		    savings
-
-		sched_mc_power_savings is dependent upon SCHED_MC, which is
-		itself architecture dependent.
-
-		sched_smt_power_savings is dependent upon SCHED_SMT, which
-		is itself architecture dependent.
-
-		The two files are independent of each other. It is possible
-		that one file may be present without the other.
-
-		Introduced by git commit 5c45bf27.
-
-
 What:		/sys/devices/system/cpu/kernel_max
 		/sys/devices/system/cpu/offline
 		/sys/devices/system/cpu/online
diff --git a/Documentation/scheduler/sched-domains.txt b/Documentation/scheduler/sched-domains.txt
@@ -61,10 +61,6 @@ The implementor should read comments in include/linux/sched.h:
 struct sched_domain fields, SD_FLAG_*, SD_*_INIT to get an idea of
 the specifics and what to tune.
 
-For SMT, the architecture must define CONFIG_SCHED_SMT and provide a
-cpumask_t cpu_sibling_map[NR_CPUS], where cpu_sibling_map[i] is the mask of
-all "i"'s siblings as well as "i" itself.
-
 Architectures may retain the regular override the default SD_*_INIT flags
 while using the generic domain builder in kernel/sched.c if they wish to
 retain the traditional SMT->SMP->NUMA topology (or some subset of that). This
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
@@ -429,8 +429,7 @@ const struct cpumask *cpu_coregroup_mask(int cpu)
 	 * For perf, we return last level cache shared map.
 	 * And for power savings, we return cpu_core_map
 	 */
-	if ((sched_mc_power_savings || sched_smt_power_savings) &&
-	    !(cpu_has(c, X86_FEATURE_AMD_DCM)))
+	if (!(cpu_has(c, X86_FEATURE_AMD_DCM)))
 		return cpu_core_mask(cpu);
 	else
 		return cpu_llc_shared_mask(cpu);
diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
@@ -330,8 +330,4 @@ void __init cpu_dev_init(void)
 		panic("Failed to register CPU subsystem");
 
 	cpu_dev_register_generic();
-
-#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
-	sched_create_sysfs_power_savings_entries(cpu_subsys.dev_root);
-#endif
 }
diff --git a/include/linux/cpu.h b/include/linux/cpu.h
@@ -36,8 +36,6 @@ extern void cpu_remove_dev_attr(struct device_attribute *attr);
 extern int cpu_add_dev_attr_group(struct attribute_group *attrs);
 extern void cpu_remove_dev_attr_group(struct attribute_group *attrs);
 
-extern int sched_create_sysfs_power_savings_entries(struct device *dev);
-
 #ifdef CONFIG_HOTPLUG_CPU
 extern void unregister_cpu(struct cpu *cpu);
 extern ssize_t arch_cpu_probe(const char *, size_t);
diff --git a/include/linux/sched.h b/include/linux/sched.h
@@ -855,61 +855,14 @@ enum cpu_idle_type {
 #define SD_WAKE_AFFINE		0x0020	/* Wake task to waking CPU */
 #define SD_PREFER_LOCAL		0x0040  /* Prefer to keep tasks local to this domain */
 #define SD_SHARE_CPUPOWER	0x0080	/* Domain members share cpu power */
-#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 */
 #define SD_OVERLAP		0x2000	/* sched_domains of this level overlap */
 
-enum powersavings_balance_level {
-	POWERSAVINGS_BALANCE_NONE = 0,  /* No power saving load balance */
-	POWERSAVINGS_BALANCE_BASIC,	/* Fill one thread/core/package
-					 * first for long running threads
-					 */
-	POWERSAVINGS_BALANCE_WAKEUP,	/* Also bias task wakeups to semi-idle
-					 * cpu package for power savings
-					 */
-	MAX_POWERSAVINGS_BALANCE_LEVELS
-};
-
-extern int sched_mc_power_savings, sched_smt_power_savings;
-
-static inline int sd_balance_for_mc_power(void)
-{
-	if (sched_smt_power_savings)
-		return SD_POWERSAVINGS_BALANCE;
-
-	if (!sched_mc_power_savings)
-		return SD_PREFER_SIBLING;
-
-	return 0;
-}
-
-static inline int sd_balance_for_package_power(void)
-{
-	if (sched_mc_power_savings | sched_smt_power_savings)
-		return SD_POWERSAVINGS_BALANCE;
-
-	return SD_PREFER_SIBLING;
-}
-
 extern int __weak arch_sd_sibiling_asym_packing(void);
 
-/*
- * Optimise SD flags for power savings:
- * SD_BALANCE_NEWIDLE helps aggressive task consolidation and power savings.
- * Keep default SD flags if sched_{smt,mc}_power_saving=0
- */
-
-static inline int sd_power_saving_flags(void)
-{
-	if (sched_mc_power_savings | sched_smt_power_savings)
-		return SD_BALANCE_NEWIDLE;
-
-	return 0;
-}
-
 struct sched_group_power {
 	atomic_t ref;
 	/*
diff --git a/include/linux/topology.h b/include/linux/topology.h
@@ -98,7 +98,6 @@ int arch_update_cpu_topology(void);
 				| 0*SD_BALANCE_WAKE			\
 				| 1*SD_WAKE_AFFINE			\
 				| 1*SD_SHARE_CPUPOWER			\
-				| 0*SD_POWERSAVINGS_BALANCE		\
 				| 1*SD_SHARE_PKG_RESOURCES		\
 				| 0*SD_SERIALIZE			\
 				| 0*SD_PREFER_SIBLING			\
@@ -134,8 +133,6 @@ int arch_update_cpu_topology(void);
 				| 0*SD_SHARE_CPUPOWER			\
 				| 1*SD_SHARE_PKG_RESOURCES		\
 				| 0*SD_SERIALIZE			\
-				| sd_balance_for_mc_power()		\
-				| sd_power_saving_flags()		\
 				,					\
 	.last_balance		= jiffies,				\
 	.balance_interval	= 1,					\
@@ -167,8 +164,6 @@ int arch_update_cpu_topology(void);
 				| 0*SD_SHARE_CPUPOWER			\
 				| 0*SD_SHARE_PKG_RESOURCES		\
 				| 0*SD_SERIALIZE			\
-				| sd_balance_for_package_power()	\
-				| sd_power_saving_flags()		\
 				,					\
 	.last_balance		= jiffies,				\
 	.balance_interval	= 1,					\
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
@@ -5929,8 +5929,6 @@ static const struct cpumask *cpu_cpu_mask(int cpu)
 	return cpumask_of_node(cpu_to_node(cpu));
 }
 
-int sched_smt_power_savings = 0, sched_mc_power_savings = 0;
-
 struct sd_data {
 	struct sched_domain **__percpu sd;
 	struct sched_group **__percpu sg;
@@ -6322,7 +6320,6 @@ sd_numa_init(struct sched_domain_topology_level *tl, int cpu)
 					| 0*SD_WAKE_AFFINE
 					| 0*SD_PREFER_LOCAL
 					| 0*SD_SHARE_CPUPOWER
-					| 0*SD_POWERSAVINGS_BALANCE
 					| 0*SD_SHARE_PKG_RESOURCES
 					| 1*SD_SERIALIZE
 					| 0*SD_PREFER_SIBLING
@@ -6819,97 +6816,6 @@ void partition_sched_domains(int ndoms_new, cpumask_var_t doms_new[],
 	mutex_unlock(&sched_domains_mutex);
 }
 
-#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
-static void reinit_sched_domains(void)
-{
-	get_online_cpus();
-
-	/* Destroy domains first to force the rebuild */
-	partition_sched_domains(0, NULL, NULL);
-
-	rebuild_sched_domains();
-	put_online_cpus();
-}
-
-static ssize_t sched_power_savings_store(const char *buf, size_t count, int smt)
-{
-	unsigned int level = 0;
-
-	if (sscanf(buf, "%u", &level) != 1)
-		return -EINVAL;
-
-	/*
-	 * level is always be positive so don't check for
-	 * level < POWERSAVINGS_BALANCE_NONE which is 0
-	 * What happens on 0 or 1 byte write,
-	 * need to check for count as well?
-	 */
-
-	if (level >= MAX_POWERSAVINGS_BALANCE_LEVELS)
-		return -EINVAL;
-
-	if (smt)
-		sched_smt_power_savings = level;
-	else
-		sched_mc_power_savings = level;
-
-	reinit_sched_domains();
-
-	return count;
-}
-
-#ifdef CONFIG_SCHED_MC
-static ssize_t sched_mc_power_savings_show(struct device *dev,
-					   struct device_attribute *attr,
-					   char *buf)
-{
-	return sprintf(buf, "%u\n", sched_mc_power_savings);
-}
-static ssize_t sched_mc_power_savings_store(struct device *dev,
-					    struct device_attribute *attr,
-					    const char *buf, size_t count)
-{
-	return sched_power_savings_store(buf, count, 0);
-}
-static DEVICE_ATTR(sched_mc_power_savings, 0644,
-		   sched_mc_power_savings_show,
-		   sched_mc_power_savings_store);
-#endif
-
-#ifdef CONFIG_SCHED_SMT
-static ssize_t sched_smt_power_savings_show(struct device *dev,
-					    struct device_attribute *attr,
-					    char *buf)
-{
-	return sprintf(buf, "%u\n", sched_smt_power_savings);
-}
-static ssize_t sched_smt_power_savings_store(struct device *dev,
-					    struct device_attribute *attr,
-					     const char *buf, size_t count)
-{
-	return sched_power_savings_store(buf, count, 1);
-}
-static DEVICE_ATTR(sched_smt_power_savings, 0644,
-		   sched_smt_power_savings_show,
-		   sched_smt_power_savings_store);
-#endif
-
-int __init sched_create_sysfs_power_savings_entries(struct device *dev)
-{
-	int err = 0;
-
-#ifdef CONFIG_SCHED_SMT
-	if (smt_capable())
-		err = device_create_file(dev, &dev_attr_sched_smt_power_savings);
-#endif
-#ifdef CONFIG_SCHED_MC
-	if (!err && mc_capable())
-		err = device_create_file(dev, &dev_attr_sched_mc_power_savings);
-#endif
-	return err;
-}
-#endif /* CONFIG_SCHED_MC || CONFIG_SCHED_SMT */
-
 /*
  * Update cpusets according to cpu_active mask.  If cpusets are
  * disabled, cpuset_update_active_cpus() becomes a simple wrapper
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
diff --git a/tools/power/cpupower/man/cpupower-set.1 b/tools/power/cpupower/man/cpupower-set.1
diff --git a/tools/power/cpupower/utils/helpers/sysfs.c b/tools/power/cpupower/utils/helpers/sysfs.c

Original file line number	Diff line number	Diff line change
`@@ -330,8 +330,4 @@ void __init cpu_dev_init(void)`
`330`	`330`	`panic("Failed to register CPU subsystem");`
`331`	`331`
`332`	`332`	`cpu_dev_register_generic();`
`333`		`-`
`334`		`-#if defined(CONFIG_SCHED_MC) \|\| defined(CONFIG_SCHED_SMT)`
`335`		`- sched_create_sysfs_power_savings_entries(cpu_subsys.dev_root);`
`336`		`-#endif`
`337`	`333`	`}`