[PATCH] sched: new sched domain for representing multi-core

Add a new sched domain for representing multi-core with shared caches
between cores.  Consider a dual package system, each package containing two
cores and with last level cache shared between cores with in a package.  If
there are two runnable processes, with this appended patch those two
processes will be scheduled on different packages.

On such systems, with this patch we have observed 8% perf improvement with
specJBB(2 warehouse) benchmark and 35% improvement with CFP2000 rate(with 2
users).

This new domain will come into play only on multi-core systems with shared
caches.  On other systems, this sched domain will be removed by domain
degeneration code.  This new domain can be also used for implementing power
savings policy (see OLS 2005 CMP kernel scheduler paper for more details..
I will post another patch for power savings policy soon)

Most of the arch/* file changes are for cpu_coregroup_map() implementation.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/i386/Kconfig

@@ -231,6 +231,15 @@ config SCHED_SMT
 	  cost of slightly increased overhead in some places. If unsure say
 	  N here.
 
+config SCHED_MC
+	bool "Multi-core scheduler support"
+	depends on SMP
+	default y
+	help
+	  Multi-core scheduler support improves the CPU scheduler's decision
+	  making when dealing with multi-core CPU chips at a cost of slightly
+	  increased overhead in some places. If unsure say N here.
+
 source "kernel/Kconfig.preempt"
 
 config X86_UP_APIC

arch/i386/kernel/cpu/common.c

@@ -266,7 +266,7 @@ static void __init early_cpu_detect(void)
 void __cpuinit generic_identify(struct cpuinfo_x86 * c)
 {
 	u32 tfms, xlvl;
-	int junk;
+	int ebx;
 
 	if (have_cpuid_p()) {
 		/* Get vendor name */
@@ -282,7 +282,7 @@ void __cpuinit generic_identify(struct cpuinfo_x86 * c)
 		/* Intel-defined flags: level 0x00000001 */
 		if ( c->cpuid_level >= 0x00000001 ) {
 			u32 capability, excap;
-			cpuid(0x00000001, &tfms, &junk, &excap, &capability);
+			cpuid(0x00000001, &tfms, &ebx, &excap, &capability);
 			c->x86_capability[0] = capability;
 			c->x86_capability[4] = excap;
 			c->x86 = (tfms >> 8) & 15;
@@ -292,6 +292,11 @@ void __cpuinit generic_identify(struct cpuinfo_x86 * c)
 			if (c->x86 >= 0x6)
 				c->x86_model += ((tfms >> 16) & 0xF) << 4;
 			c->x86_mask = tfms & 15;
+#ifdef CONFIG_SMP
+			c->apicid = phys_pkg_id((ebx >> 24) & 0xFF, 0);
+#else
+			c->apicid = (ebx >> 24) & 0xFF;
+#endif
 		} else {
 			/* Have CPUID level 0 only - unheard of */
 			c->x86 = 4;
@@ -474,7 +479,6 @@ void __cpuinit detect_ht(struct cpuinfo_x86 *c)
 
 	cpuid(1, &eax, &ebx, &ecx, &edx);
 
-	c->apicid = phys_pkg_id((ebx >> 24) & 0xFF, 0);
 
 	if (!cpu_has(c, X86_FEATURE_HT) || cpu_has(c, X86_FEATURE_CMP_LEGACY))
 		return;

arch/i386/kernel/cpu/intel_cacheinfo.c

@@ -173,6 +173,10 @@ unsigned int __cpuinit init_intel_cacheinfo(struct cpuinfo_x86 *c)
 	unsigned int trace = 0, l1i = 0, l1d = 0, l2 = 0, l3 = 0; /* Cache sizes */
 	unsigned int new_l1d = 0, new_l1i = 0; /* Cache sizes from cpuid(4) */
 	unsigned int new_l2 = 0, new_l3 = 0, i; /* Cache sizes from cpuid(4) */
+	unsigned int l2_id = 0, l3_id = 0, num_threads_sharing, index_msb;
+#ifdef CONFIG_SMP
+	unsigned int cpu = (c == &boot_cpu_data) ? 0 : (c - cpu_data);
+#endif
 
 	if (c->cpuid_level > 3) {
 		static int is_initialized;
@@ -205,9 +209,15 @@ unsigned int __cpuinit init_intel_cacheinfo(struct cpuinfo_x86 *c)
 					break;
 				    case 2:
 					new_l2 = this_leaf.size/1024;
+					num_threads_sharing = 1 + this_leaf.eax.split.num_threads_sharing;
+					index_msb = get_count_order(num_threads_sharing);
+					l2_id = c->apicid >> index_msb;
 					break;
 				    case 3:
 					new_l3 = this_leaf.size/1024;
+					num_threads_sharing = 1 + this_leaf.eax.split.num_threads_sharing;
+					index_msb = get_count_order(num_threads_sharing);
+					l3_id = c->apicid >> index_msb;
 					break;
 				    default:
 					break;
@@ -273,11 +283,19 @@ unsigned int __cpuinit init_intel_cacheinfo(struct cpuinfo_x86 *c)
 		if (new_l1i)
 			l1i = new_l1i;
 
-		if (new_l2)
+		if (new_l2) {
 			l2 = new_l2;
+#ifdef CONFIG_SMP
+			cpu_llc_id[cpu] = l2_id;
+#endif
+		}
 
-		if (new_l3)
+		if (new_l3) {
 			l3 = new_l3;
+#ifdef CONFIG_SMP
+			cpu_llc_id[cpu] = l3_id;
+#endif
+		}
 
 		if ( trace )
 			printk (KERN_INFO "CPU: Trace cache: %dK uops", trace);

arch/i386/kernel/smpboot.c

@@ -72,6 +72,9 @@ int phys_proc_id[NR_CPUS] __read_mostly = {[0 ... NR_CPUS-1] = BAD_APICID};
 /* Core ID of each logical CPU */
 int cpu_core_id[NR_CPUS] __read_mostly = {[0 ... NR_CPUS-1] = BAD_APICID};
 
+/* Last level cache ID of each logical CPU */
+int cpu_llc_id[NR_CPUS] __cpuinitdata = {[0 ... NR_CPUS-1] = BAD_APICID};
+
 /* representing HT siblings of each logical CPU */
 cpumask_t cpu_sibling_map[NR_CPUS] __read_mostly;
 EXPORT_SYMBOL(cpu_sibling_map);
@@ -440,6 +443,18 @@ static void __devinit smp_callin(void)
 
 static int cpucount;
 
+/* maps the cpu to the sched domain representing multi-core */
+cpumask_t cpu_coregroup_map(int cpu)
+{
+	struct cpuinfo_x86 *c = cpu_data + cpu;
+	/*
+	 * For perf, we return last level cache shared map.
+	 * TBD: when power saving sched policy is added, we will return
+	 *      cpu_core_map when power saving policy is enabled
+	 */
+	return c->llc_shared_map;
+}
+
 /* representing cpus for which sibling maps can be computed */
 static cpumask_t cpu_sibling_setup_map;
 
@@ -459,19 +474,28 @@ set_cpu_sibling_map(int cpu)
 				cpu_set(cpu, cpu_sibling_map[i]);
 				cpu_set(i, cpu_core_map[cpu]);
 				cpu_set(cpu, cpu_core_map[i]);
+				cpu_set(i, c[cpu].llc_shared_map);
+				cpu_set(cpu, c[i].llc_shared_map);
 			}
 		}
 	} else {
 		cpu_set(cpu, cpu_sibling_map[cpu]);
 	}
 
+	cpu_set(cpu, c[cpu].llc_shared_map);
+
 	if (current_cpu_data.x86_max_cores == 1) {
 		cpu_core_map[cpu] = cpu_sibling_map[cpu];
 		c[cpu].booted_cores = 1;
 		return;
 	}
 
 	for_each_cpu_mask(i, cpu_sibling_setup_map) {
+		if (cpu_llc_id[cpu] != BAD_APICID &&
+		    cpu_llc_id[cpu] == cpu_llc_id[i]) {
+			cpu_set(i, c[cpu].llc_shared_map);
+			cpu_set(cpu, c[i].llc_shared_map);
+		}
 		if (phys_proc_id[cpu] == phys_proc_id[i]) {
 			cpu_set(i, cpu_core_map[cpu]);
 			cpu_set(cpu, cpu_core_map[i]);

arch/x86_64/Kconfig

@@ -250,6 +250,15 @@ config SCHED_SMT
 	  cost of slightly increased overhead in some places. If unsure say
 	  N here.
 
+config SCHED_MC
+	bool "Multi-core scheduler support"
+	depends on SMP
+	default y
+	help
+	  Multi-core scheduler support improves the CPU scheduler's decision
+	  making when dealing with multi-core CPU chips at a cost of slightly
+	  increased overhead in some places. If unsure say N here.
+
 source "kernel/Kconfig.preempt"
 
 config NUMA

arch/x86_64/kernel/setup.c

@@ -962,7 +962,6 @@ static void __cpuinit detect_ht(struct cpuinfo_x86 *c)
 
 	cpuid(1, &eax, &ebx, &ecx, &edx);
 
-	c->apicid = phys_pkg_id(0);
 
 	if (!cpu_has(c, X86_FEATURE_HT) || cpu_has(c, X86_FEATURE_CMP_LEGACY))
 		return;
@@ -1171,6 +1170,8 @@ void __cpuinit identify_cpu(struct cpuinfo_x86 *c)
 			c->x86_capability[2] = cpuid_edx(0x80860001);
 	}
 
+	c->apicid = phys_pkg_id(0);
+
 	/*
 	 * Vendor-specific initialization.  In this section we
 	 * canonicalize the feature flags, meaning if there are

arch/x86_64/kernel/smpboot.c

@@ -68,6 +68,9 @@ u8 phys_proc_id[NR_CPUS] __read_mostly = { [0 ... NR_CPUS-1] = BAD_APICID };
 /* core ID of each logical CPU */
 u8 cpu_core_id[NR_CPUS] __read_mostly = { [0 ... NR_CPUS-1] = BAD_APICID };
 
+/* Last level cache ID of each logical CPU */
+u8 cpu_llc_id[NR_CPUS] __cpuinitdata  = {[0 ... NR_CPUS-1] = BAD_APICID};
+
 /* Bitmask of currently online CPUs */
 cpumask_t cpu_online_map __read_mostly;
 
@@ -445,6 +448,18 @@ void __cpuinit smp_callin(void)
 	cpu_set(cpuid, cpu_callin_map);
 }
 
+/* maps the cpu to the sched domain representing multi-core */
+cpumask_t cpu_coregroup_map(int cpu)
+{
+	struct cpuinfo_x86 *c = cpu_data + cpu;
+	/*
+	 * For perf, we return last level cache shared map.
+	 * TBD: when power saving sched policy is added, we will return
+	 *      cpu_core_map when power saving policy is enabled
+	 */
+	return c->llc_shared_map;
+}
+
 /* representing cpus for which sibling maps can be computed */
 static cpumask_t cpu_sibling_setup_map;
 
@@ -463,19 +478,28 @@ static inline void set_cpu_sibling_map(int cpu)
 				cpu_set(cpu, cpu_sibling_map[i]);
 				cpu_set(i, cpu_core_map[cpu]);
 				cpu_set(cpu, cpu_core_map[i]);
+				cpu_set(i, c[cpu].llc_shared_map);
+				cpu_set(cpu, c[i].llc_shared_map);
 			}
 		}
 	} else {
 		cpu_set(cpu, cpu_sibling_map[cpu]);
 	}
 
+	cpu_set(cpu, c[cpu].llc_shared_map);
+
 	if (current_cpu_data.x86_max_cores == 1) {
 		cpu_core_map[cpu] = cpu_sibling_map[cpu];
 		c[cpu].booted_cores = 1;
 		return;
 	}
 
 	for_each_cpu_mask(i, cpu_sibling_setup_map) {
+		if (cpu_llc_id[cpu] != BAD_APICID &&
+		    cpu_llc_id[cpu] == cpu_llc_id[i]) {
+			cpu_set(i, c[cpu].llc_shared_map);
+			cpu_set(cpu, c[i].llc_shared_map);
+		}
 		if (phys_proc_id[cpu] == phys_proc_id[i]) {
 			cpu_set(i, cpu_core_map[cpu]);
 			cpu_set(cpu, cpu_core_map[i]);

include/asm-i386/processor.h

@@ -20,6 +20,7 @@
 #include <linux/config.h>
 #include <linux/threads.h>
 #include <asm/percpu.h>
+#include <linux/cpumask.h>
 
 /* flag for disabling the tsc */
 extern int tsc_disable;
@@ -67,6 +68,9 @@ struct cpuinfo_x86 {
 	char	pad0;
 	int	x86_power;
 	unsigned long loops_per_jiffy;
+#ifdef CONFIG_SMP
+	cpumask_t llc_shared_map;	/* cpus sharing the last level cache */
+#endif
 	unsigned char x86_max_cores;	/* cpuid returned max cores value */
 	unsigned char booted_cores;	/* number of cores as seen by OS */
 	unsigned char apicid;
@@ -103,6 +107,7 @@ extern struct cpuinfo_x86 cpu_data[];
 
 extern	int phys_proc_id[NR_CPUS];
 extern	int cpu_core_id[NR_CPUS];
+extern	int cpu_llc_id[NR_CPUS];
 extern char ignore_fpu_irq;
 
 extern void identify_cpu(struct cpuinfo_x86 *);

include/asm-i386/topology.h

@@ -112,4 +112,6 @@ extern unsigned long node_remap_size[];
 
 #endif /* CONFIG_NUMA */
 
+extern cpumask_t cpu_coregroup_map(int cpu);
+
 #endif /* _ASM_I386_TOPOLOGY_H */

include/asm-x86_64/processor.h

@@ -20,6 +20,7 @@
 #include <asm/mmsegment.h>
 #include <asm/percpu.h>
 #include <linux/personality.h>
+#include <linux/cpumask.h>
 
 #define TF_MASK		0x00000100
 #define IF_MASK		0x00000200
@@ -65,6 +66,9 @@ struct cpuinfo_x86 {
         __u32   x86_power; 	
 	__u32   extended_cpuid_level;	/* Max extended CPUID function supported */
 	unsigned long loops_per_jiffy;
+#ifdef CONFIG_SMP
+	cpumask_t llc_shared_map;	/* cpus sharing the last level cache */
+#endif
 	__u8	apicid;
 	__u8	booted_cores;	/* number of cores as seen by OS */
 } ____cacheline_aligned;

include/asm-x86_64/smp.h

@@ -56,6 +56,7 @@ extern cpumask_t cpu_sibling_map[NR_CPUS];
 extern cpumask_t cpu_core_map[NR_CPUS];
 extern u8 phys_proc_id[NR_CPUS];
 extern u8 cpu_core_id[NR_CPUS];
+extern u8 cpu_llc_id[NR_CPUS];
 
 #define SMP_TRAMPOLINE_BASE 0x6000
 

include/asm-x86_64/topology.h

@@ -68,4 +68,6 @@ extern int __node_distance(int, int);
 
 #include <asm-generic/topology.h>
 
+extern cpumask_t cpu_coregroup_map(int cpu);
+
 #endif

include/linux/topology.h

@@ -164,6 +164,15 @@
 	.nr_balance_failed	= 0,			\
 }
 
+#ifdef CONFIG_SCHED_MC
+#ifndef SD_MC_INIT
+/* for now its same as SD_CPU_INIT.
+ * TBD: Tune Domain parameters!
+ */
+#define SD_MC_INIT   SD_CPU_INIT
+#endif
+#endif
+
 #ifdef CONFIG_NUMA
 #ifndef SD_NODE_INIT
 #error Please define an appropriate SD_NODE_INIT in include/asm/topology.h!!!