Re: [PATCH][RFC] make cpu_sibling_map a cpumask_t

Zwane Mwaikambo
2003-12-08T20:52:44Z

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On Mon, 8 Dec 2003, Nick Piggin wrote:

> It turns the cpu_sibling_map array from an array of cpus to an array
> of cpumasks. This allows handling of more than 2 siblings, not that
> I know of any immediate need.
>
> I think it generalises cpu_sibling_map sufficiently that it can become
> generic code. This would allow architecture specific code to build the
> sibling map, and then Ingo's or my HT implementations to build their
> scheduling descriptions in generic code.
>
> I'm not aware of any reason why the kernel should not become generally
> SMT aware. It is sufficiently different to SMP that it is worth
> specialising it, although I am only aware of P4 and POWER5 implementations.

Generally i agree, it's fairly unintrusive and appears to clean up some
things. Perhaps Andrew will take it a bit later after release.

> P.S.
> I have an alternative to Ingo's HT scheduler which basically does
> the same thing. It is showing a 20% elapsed time improvement with a
> make -j3 on a 2xP4 Xeon (4 logical CPUs).

-j3 is an odd number, what does -j4, -j8, -j16 look like?

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linux-2.6-npiggin/arch/i386/kernel/cpu/cpufreq/p4-clockmod.c | 9 --
linux-2.6-npiggin/arch/i386/kernel/io_apic.c | 19 ++--
linux-2.6-npiggin/arch/i386/kernel/smpboot.c | 46 +++++------
linux-2.6-npiggin/arch/i386/oprofile/op_model_p4.c | 7 -
linux-2.6-npiggin/include/asm-i386/smp.h | 2
5 files changed, 37 insertions(+), 46 deletions(-)

diff -puN include/asm-i386/smp.h~sibling-map-to-cpumask include/asm-i386/smp.h
--- linux-2.6/include/asm-i386/smp.h~sibling-map-to-cpumask 2003-12-08 14:42:28.000000000 +1100
+++ linux-2.6-npiggin/include/asm-i386/smp.h 2003-12-08 14:42:28.000000000 +1100
@@ -34,7 +34,7 @@
extern void smp_alloc_memory(void);
extern int pic_mode;
extern int smp_num_siblings;
-extern int cpu_sibling_map[];
+extern cpumask_t cpu_sibling_map[];

extern void smp_flush_tlb(void);
extern void smp_message_irq(int cpl, void *dev_id, struct pt_regs *regs);
diff -puN arch/i386/kernel/smpboot.c~sibling-map-to-cpumask arch/i386/kernel/smpboot.c
--- linux-2.6/arch/i386/kernel/smpboot.c~sibling-map-to-cpumask 2003-12-08 14:42:28.000000000 +1100
+++ linux-2.6-npiggin/arch/i386/kernel/smpboot.c 2003-12-08 15:07:48.000000000 +1100
@@ -933,7 +933,7 @@ static int boot_cpu_logical_apicid;
/* Where the IO area was mapped on multiquad, always 0 otherwise */
void *xquad_portio;

-int cpu_sibling_map[NR_CPUS] __cacheline_aligned;
+cpumask_t cpu_sibling_map[NR_CPUS] __cacheline_aligned;

static void __init smp_boot_cpus(unsigned int max_cpus)
{
@@ -1079,32 +1079,28 @@ static void __init smp_boot_cpus(unsigne
Dprintk("Boot done.\n");

/*
- * If Hyper-Threading is avaialble, construct cpu_sibling_map[], so
- * that we can tell the sibling CPU efficiently.
+ * construct cpu_sibling_map[], so that we can tell sibling CPUs
+ * efficiently.
*/
- if (cpu_has_ht && smp_num_siblings > 1) {
- for (cpu = 0; cpu < NR_CPUS; cpu++)
- cpu_sibling_map[cpu] = NO_PROC_ID;
-
- for (cpu = 0; cpu < NR_CPUS; cpu++) {
- int i;
- if (!cpu_isset(cpu, cpu_callout_map))
- continue;
+ for (cpu = 0; cpu < NR_CPUS; cpu++)
+ cpu_sibling_map[cpu] = CPU_MASK_NONE;

- for (i = 0; i < NR_CPUS; i++) {
- if (i == cpu || !cpu_isset(i, cpu_callout_map))
- continue;
- if (phys_proc_id[cpu] == phys_proc_id[i]) {
- cpu_sibling_map[cpu] = i;
- printk("cpu_sibling_map[%d] = %d\n", cpu, cpu_sibling_map[cpu]);
- break;
- }
- }
- if (cpu_sibling_map[cpu] == NO_PROC_ID) {
- smp_num_siblings = 1;
- printk(KERN_WARNING "WARNING: No sibling found for CPU %d.\n", cpu);
+ for (cpu = 0; cpu < NR_CPUS; cpu++) {
+ int siblings = 0;
+ int i;
+ if (!cpu_isset(cpu, cpu_callout_map))
+ continue;
+
+ for (i = 0; i < NR_CPUS; i++) {
+ if (!cpu_isset(i, cpu_callout_map))
+ continue;
+ if (phys_proc_id[cpu] == phys_proc_id[i]) {
+ siblings++;
+ cpu_set(i, cpu_sibling_map[cpu]);
}
}
+ if (siblings != smp_num_siblings)
+ printk(KERN_WARNING "WARNING: %d siblings found for CPU%d, should be %d\n", siblings, cpu, smp_num_siblings);
}

smpboot_setup_io_apic();
@@ -1143,8 +1139,8 @@ __init void arch_init_sched_domains(void

*cpu_domain = SD_CPU_INIT;
cpu_domain->span = CPU_MASK_NONE;
- cpu_set(i, cpu_domain->span);
- cpu_set(cpu_sibling_map[i], cpu_domain->span);
+ cpu_domain->span = cpu_sibling_map[i];
+ WARN_ON(!cpu_isset(i, cpu_sibling_map[i]));
cpu_domain->flags |= SD_FLAG_WAKE | SD_FLAG_IDLE;
cpu_domain->cache_hot_time = 0;
cpu_domain->cache_nice_tries = 0;
diff -puN arch/i386/kernel/io_apic.c~sibling-map-to-cpumask arch/i386/kernel/io_apic.c
--- linux-2.6/arch/i386/kernel/io_apic.c~sibling-map-to-cpumask 2003-12-08 14:42:28.000000000 +1100
+++ linux-2.6-npiggin/arch/i386/kernel/io_apic.c 2003-12-08 14:42:28.000000000 +1100
@@ -309,8 +309,7 @@ struct irq_cpu_info {

#define IRQ_ALLOWED(cpu, allowed_mask) cpu_isset(cpu, allowed_mask)

-#define CPU_TO_PACKAGEINDEX(i) \
- ((physical_balance && i > cpu_sibling_map[i]) ? cpu_sibling_map[i] : i)
+#define CPU_TO_PACKAGEINDEX(i) (first_cpu(cpu_sibling_map[i]))

#define MAX_BALANCED_IRQ_INTERVAL (5*HZ)
#define MIN_BALANCED_IRQ_INTERVAL (HZ/2)
@@ -393,6 +392,7 @@ static void do_irq_balance(void)
unsigned long max_cpu_irq = 0, min_cpu_irq = (~0);
unsigned long move_this_load = 0;
int max_loaded = 0, min_loaded = 0;
+ int load;
unsigned long useful_load_threshold = balanced_irq_interval + 10;
int selected_irq;
int tmp_loaded, first_attempt = 1;
@@ -444,7 +444,7 @@ static void do_irq_balance(void)
for (i = 0; i < NR_CPUS; i++) {
if (!cpu_online(i))
continue;
- if (physical_balance && i > cpu_sibling_map[i])
+ if (i != CPU_TO_PACKAGEINDEX(i))
continue;
if (min_cpu_irq > CPU_IRQ(i)) {
min_cpu_irq = CPU_IRQ(i);
@@ -463,7 +463,7 @@ tryanothercpu:
for (i = 0; i < NR_CPUS; i++) {
if (!cpu_online(i))
continue;
- if (physical_balance && i > cpu_sibling_map[i])
+ if (i != CPU_TO_PACKAGEINDEX(i))
continue;
if (max_cpu_irq <= CPU_IRQ(i))
continue;
@@ -543,9 +543,14 @@ tryanotherirq:
* We seek the least loaded sibling by making the comparison
* (A+B)/2 vs B
*/
- if (physical_balance && (CPU_IRQ(min_loaded) >> 1) >
- CPU_IRQ(cpu_sibling_map[min_loaded]))
- min_loaded = cpu_sibling_map[min_loaded];
+ load = CPU_IRQ(min_loaded) >> 1;
+ for_each_cpu(j, cpu_sibling_map[min_loaded]) {
+ if (load > CPU_IRQ(j)) {
+ /* This won't change cpu_sibling_map[min_loaded] */
+ load = CPU_IRQ(j);
+ min_loaded = j;
+ }
+ }

cpus_and(allowed_mask, cpu_online_map, irq_affinity[selected_irq]);
target_cpu_mask = cpumask_of_cpu(min_loaded);
diff -puN arch/i386/kernel/cpu/cpufreq/p4-clockmod.c~sibling-map-to-cpumask arch/i386/kernel/cpu/cpufreq/p4-clockmod.c
--- linux-2.6/arch/i386/kernel/cpu/cpufreq/p4-clockmod.c~sibling-map-to-cpumask 2003-12-08 14:42:28.000000000 +1100
+++ linux-2.6-npiggin/arch/i386/kernel/cpu/cpufreq/p4-clockmod.c 2003-12-08 14:42:28.000000000 +1100
@@ -67,14 +67,7 @@ static int cpufreq_p4_setdc(unsigned int
cpus_allowed = current->cpus_allowed;

/* only run on CPU to be set, or on its sibling */
- affected_cpu_map = cpumask_of_cpu(cpu);
-#ifdef CONFIG_X86_HT
- hyperthreading = ((cpu_has_ht) && (smp_num_siblings == 2));
- if (hyperthreading) {
- sibling = cpu_sibling_map[cpu];
- cpu_set(sibling, affected_cpu_map);
- }
-#endif
+ affected_cpu_map = cpu_sibling_map[cpu];
set_cpus_allowed(current, affected_cpu_map);
BUG_ON(!cpu_isset(smp_processor_id(), affected_cpu_map));

diff -puN arch/i386/oprofile/op_model_p4.c~sibling-map-to-cpumask arch/i386/oprofile/op_model_p4.c
--- linux-2.6/arch/i386/oprofile/op_model_p4.c~sibling-map-to-cpumask 2003-12-08 14:42:28.000000000 +1100
+++ linux-2.6-npiggin/arch/i386/oprofile/op_model_p4.c 2003-12-08 14:42:28.000000000 +1100
@@ -382,11 +382,8 @@ static struct p4_event_binding p4_events
static unsigned int get_stagger(void)
{
#ifdef CONFIG_SMP
- int cpu;
- if (smp_num_siblings > 1) {
- cpu = smp_processor_id();
- return (cpu_sibling_map[cpu] > cpu) ? 0 : 1;
- }
+ int cpu = smp_processor_id();
+ return (cpu != first_cpu(cpu_sibling_map[cpu]));
#endif
return 0;
}

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