[patch 36/47] Allocate and free cpu lowcores and stacks when needed/possible.

Martin Schwidefsky
2007-12-20T15:34:40Z

[-- Attachment #1: 135-cpu-lowcores.diff --]
[-- Type: text/plain, Size: 5398 bytes --]

From: Heiko Carstens <heiko.carstens@de.ibm.com>

No need to preallocate the per cpu lowcores and stacks.
Savings are 28-32k per offline cpu.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
---

arch/s390/kernel/smp.c | 106 +++++++++++++++++++++++++++++++++----------------
1 file changed, 72 insertions(+), 34 deletions(-)

Index: quilt-2.6/arch/s390/kernel/smp.c
===================================================================
--- quilt-2.6.orig/arch/s390/kernel/smp.c
+++ quilt-2.6/arch/s390/kernel/smp.c
@@ -589,8 +589,72 @@ static void __init smp_create_idle(unsig
spin_lock_init(&(&per_cpu(s390_idle, cpu))->lock);
}

+static int __cpuinit smp_alloc_lowcore(int cpu)
+{
+ unsigned long async_stack, panic_stack;
+ struct _lowcore *lowcore;
+ int lc_order;
+
+ lc_order = sizeof(long) == 8 ? 1 : 0;
+ lowcore = (void *) __get_free_pages(GFP_KERNEL | GFP_DMA, lc_order);
+ if (!lowcore)
+ return -ENOMEM;
+ async_stack = __get_free_pages(GFP_KERNEL, ASYNC_ORDER);
+ if (!async_stack)
+ goto out_async_stack;
+ panic_stack = __get_free_page(GFP_KERNEL);
+ if (!panic_stack)
+ goto out_panic_stack;
+
+ *lowcore = S390_lowcore;
+ lowcore->async_stack = async_stack + ASYNC_SIZE;
+ lowcore->panic_stack = panic_stack + PAGE_SIZE;
+
+#ifndef CONFIG_64BIT
+ if (MACHINE_HAS_IEEE) {
+ unsigned long save_area;
+
+ save_area = get_zeroed_page(GFP_KERNEL);
+ if (!save_area)
+ goto out_save_area;
+ lowcore->extended_save_area_addr = (u32) save_area;
+ }
+#endif
+ lowcore_ptr[cpu] = lowcore;
+ return 0;
+
+#ifndef CONFIG_64BIT
+out_save_area:
+ free_page(panic_stack);
+#endif
+out_panic_stack:
+ free_pages(async_stack, ASYNC_ORDER);
+out_async_stack:
+ free_pages((unsigned long) lowcore, lc_order);
+ return -ENOMEM;
+}
+
+#ifdef CONFIG_HOTPLUG_CPU
+static void smp_free_lowcore(int cpu)
+{
+ struct _lowcore *lowcore;
+ int lc_order;
+
+ lc_order = sizeof(long) == 8 ? 1 : 0;
+ lowcore = lowcore_ptr[cpu];
+#ifndef CONFIG_64BIT
+ if (MACHINE_HAS_IEEE)
+ free_page((unsigned long) lowcore->extended_save_area_addr);
+#endif
+ free_page(lowcore->panic_stack - PAGE_SIZE);
+ free_pages(lowcore->async_stack - ASYNC_SIZE, ASYNC_ORDER);
+ free_pages((unsigned long) lowcore, lc_order);
+ lowcore_ptr[cpu] = NULL;
+}
+#endif /* CONFIG_HOTPLUG_CPU */
+
/* Upping and downing of CPUs */
-int __cpu_up(unsigned int cpu)
+int __cpuinit __cpu_up(unsigned int cpu)
{
struct task_struct *idle;
struct _lowcore *cpu_lowcore;
@@ -599,6 +663,8 @@ int __cpu_up(unsigned int cpu)

if (smp_cpu_state[cpu] != CPU_STATE_CONFIGURED)
return -EIO;
+ if (smp_alloc_lowcore(cpu))
+ return -ENOMEM;

ccode = signal_processor_p((__u32)(unsigned long)(lowcore_ptr[cpu]),
cpu, sigp_set_prefix);
@@ -613,6 +679,7 @@ int __cpu_up(unsigned int cpu)
cpu_lowcore = lowcore_ptr[cpu];
cpu_lowcore->kernel_stack = (unsigned long)
task_stack_page(idle) + THREAD_SIZE;
+ cpu_lowcore->thread_info = (unsigned long) task_thread_info(idle);
sf = (struct stack_frame *) (cpu_lowcore->kernel_stack
- sizeof(struct pt_regs)
- sizeof(struct stack_frame));
@@ -626,6 +693,8 @@ int __cpu_up(unsigned int cpu)
cpu_lowcore->percpu_offset = __per_cpu_offset[cpu];
cpu_lowcore->current_task = (unsigned long) idle;
cpu_lowcore->cpu_data.cpu_nr = cpu;
+ cpu_lowcore->softirq_pending = 0;
+ cpu_lowcore->ext_call_fast = 0;
eieio();

while (signal_processor(cpu, sigp_restart) == sigp_busy)
@@ -686,6 +755,7 @@ void __cpu_die(unsigned int cpu)
/* Wait until target cpu is down */
while (!smp_cpu_not_running(cpu))
cpu_relax();
+ smp_free_lowcore(cpu);
printk(KERN_INFO "Processor %d spun down\n", cpu);
}

@@ -699,15 +769,9 @@ void cpu_die(void)

#endif /* CONFIG_HOTPLUG_CPU */

-/*
- * Cycle through the processors and setup structures.
- */
-
void __init smp_prepare_cpus(unsigned int max_cpus)
{
- unsigned long stack;
unsigned int cpu;
- int i;

smp_detect_cpus();

@@ -715,35 +779,9 @@ void __init smp_prepare_cpus(unsigned in
if (register_external_interrupt(0x1201, do_ext_call_interrupt) != 0)
panic("Couldn't request external interrupt 0x1201");
memset(lowcore_ptr, 0, sizeof(lowcore_ptr));
- /*
- * Initialize prefix pages and stacks for all possible cpus
- */
print_cpu_info(&S390_lowcore.cpu_data);
+ smp_alloc_lowcore(smp_processor_id());

- for_each_possible_cpu(i) {
- lowcore_ptr[i] = (struct _lowcore *)
- __get_free_pages(GFP_KERNEL | GFP_DMA,
- sizeof(void*) == 8 ? 1 : 0);
- stack = __get_free_pages(GFP_KERNEL, ASYNC_ORDER);
- if (!lowcore_ptr[i] || !stack)
- panic("smp_boot_cpus failed to allocate memory\n");
-
- *(lowcore_ptr[i]) = S390_lowcore;
- lowcore_ptr[i]->async_stack = stack + ASYNC_SIZE;
- stack = __get_free_pages(GFP_KERNEL, 0);
- if (!stack)
- panic("smp_boot_cpus failed to allocate memory\n");
- lowcore_ptr[i]->panic_stack = stack + PAGE_SIZE;
-#ifndef CONFIG_64BIT
- if (MACHINE_HAS_IEEE) {
- lowcore_ptr[i]->extended_save_area_addr =
- (__u32) __get_free_pages(GFP_KERNEL, 0);
- if (!lowcore_ptr[i]->extended_save_area_addr)
- panic("smp_boot_cpus failed to "
- "allocate memory\n");
- }
-#endif
- }
#ifndef CONFIG_64BIT
if (MACHINE_HAS_IEEE)
ctl_set_bit(14, 29); /* enable extended save area */