[ARM SMP] Add core ARM support for local timers
Add infrastructure for supporting per-cpu local timers to update
the profiling information and update system time accounting.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 91d5ef3..3bfef09 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -356,6 +356,16 @@
Say Y here to experiment with turning CPUs off and on. CPUs
can be controlled through /sys/devices/system/cpu.
+config LOCAL_TIMERS
+ bool "Use local timer interrupts"
+ depends on SMP && n
+ default y
+ help
+ Enable support for local timers on SMP platforms, rather then the
+ legacy IPI broadcast method. Local timers allows the system
+ accounting to be spread across the timer interval, preventing a
+ "thundering herd" at every timer tick.
+
config PREEMPT
bool "Preemptible Kernel (EXPERIMENTAL)"
depends on EXPERIMENTAL
diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index a511ec5..d9fb819 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -47,6 +47,13 @@
movne r0, sp
adrne lr, 1b
bne do_IPI
+
+#ifdef CONFIG_LOCAL_TIMERS
+ test_for_ltirq r0, r6, r5, lr
+ movne r0, sp
+ adrne lr, 1b
+ bne do_local_timer
+#endif
#endif
.endm
diff --git a/arch/arm/kernel/irq.c b/arch/arm/kernel/irq.c
index 6f86d0a..d7099db 100644
--- a/arch/arm/kernel/irq.c
+++ b/arch/arm/kernel/irq.c
@@ -264,6 +264,7 @@
#endif
#ifdef CONFIG_SMP
show_ipi_list(p);
+ show_local_irqs(p);
#endif
seq_printf(p, "Err: %10lu\n", irq_err_count);
}
diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index f5fc57e..77e2e9c 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -185,6 +185,11 @@
migrate_irqs();
/*
+ * Stop the local timer for this CPU.
+ */
+ local_timer_stop(cpu);
+
+ /*
* Flush user cache and TLB mappings, and then remove this CPU
* from the vm mask set of all processes.
*/
@@ -290,6 +295,11 @@
cpu_set(cpu, cpu_online_map);
/*
+ * Setup local timer for this CPU.
+ */
+ local_timer_setup(cpu);
+
+ /*
* OK, it's off to the idle thread for us
*/
cpu_idle();
@@ -454,6 +464,18 @@
seq_putc(p, '\n');
}
+void show_local_irqs(struct seq_file *p)
+{
+ unsigned int cpu;
+
+ seq_printf(p, "LOC: ");
+
+ for_each_present_cpu(cpu)
+ seq_printf(p, "%10u ", irq_stat[cpu].local_timer_irqs);
+
+ seq_putc(p, '\n');
+}
+
static void ipi_timer(struct pt_regs *regs)
{
int user = user_mode(regs);
@@ -464,6 +486,18 @@
irq_exit();
}
+#ifdef CONFIG_LOCAL_TIMERS
+asmlinkage void do_local_timer(struct pt_regs *regs)
+{
+ int cpu = smp_processor_id();
+
+ if (local_timer_ack()) {
+ irq_stat[cpu].local_timer_irqs++;
+ ipi_timer(regs);
+ }
+}
+#endif
+
/*
* ipi_call_function - handle IPI from smp_call_function()
*