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Commit f230886b authored by Heiko Carstens's avatar Heiko Carstens Committed by Martin Schwidefsky
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[S390] smp: delay idle task creation 



Delay idle task creation until a cpu gets set online instead of
creating them for all possible cpus at system startup.
For one cpu system this should safe more than 1 MB.
On my debug system with lots of debug stuff enabled this saves 2 MB.

Same as on x86.

Signed-off-by: default avatarHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent 09a8e7ad

arch/s390/kernel/smp.c

+26 −15
Original line number Diff line number Diff line
@@ -23,6 +23,7 @@ 
#define KMSG_COMPONENT "cpu"

#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt



#include <linux/workqueue.h>

#include <linux/module.h>

#include <linux/init.h>

#include <linux/mm.h>
@@ -477,18 +478,20 @@ int __cpuinit start_secondary(void *cpuvoid) 
	return 0;

}



static void __init smp_create_idle(unsigned int cpu)

struct create_idle {

	struct work_struct work;

	struct task_struct *idle;

	struct completion done;

	int cpu;

};



static void __cpuinit smp_fork_idle(struct work_struct *work)

{

	struct task_struct *p;

	struct create_idle *c_idle;



	/*

	 *  don't care about the psw and regs settings since we'll never

	 *  reschedule the forked task.

	 */

	p = fork_idle(cpu);

	if (IS_ERR(p))

		panic("failed fork for CPU %u: %li", cpu, PTR_ERR(p));

	current_set[cpu] = p;

	c_idle = container_of(work, struct create_idle, work);

	c_idle->idle = fork_idle(c_idle->cpu);

	complete(&c_idle->done);

}



static int __cpuinit smp_alloc_lowcore(int cpu)
@@ -552,6 +555,7 @@ static void smp_free_lowcore(int cpu) 
int __cpuinit __cpu_up(unsigned int cpu)

{

	struct _lowcore *cpu_lowcore;

	struct create_idle c_idle;

	struct task_struct *idle;

	struct stack_frame *sf;

	u32 lowcore;
@@ -559,6 +563,18 @@ int __cpuinit __cpu_up(unsigned int cpu) 


	if (smp_cpu_state[cpu] != CPU_STATE_CONFIGURED)

		return -EIO;

	idle = current_set[cpu];

	if (!idle) {

		c_idle.done = COMPLETION_INITIALIZER_ONSTACK(c_idle.done);

		INIT_WORK_ONSTACK(&c_idle.work, smp_fork_idle);

		c_idle.cpu = cpu;

		schedule_work(&c_idle.work);

		wait_for_completion(&c_idle.done);

		if (IS_ERR(c_idle.idle))

			return PTR_ERR(c_idle.idle);

		idle = c_idle.idle;

		current_set[cpu] = c_idle.idle;

	}

	if (smp_alloc_lowcore(cpu))

		return -ENOMEM;

	do {
@@ -573,7 +589,6 @@ int __cpuinit __cpu_up(unsigned int cpu) 
	while (sigp_p(lowcore, cpu, sigp_set_prefix) == sigp_busy)

		udelay(10);



	idle = current_set[cpu];

	cpu_lowcore = lowcore_ptr[cpu];

	cpu_lowcore->kernel_stack = (unsigned long)

		task_stack_page(idle) + THREAD_SIZE;
@@ -685,7 +700,6 @@ void __init smp_prepare_cpus(unsigned int max_cpus) 
#endif

	unsigned long async_stack, panic_stack;

	struct _lowcore *lowcore;

	unsigned int cpu;



	smp_detect_cpus();
@@ -720,9 +734,6 @@ void __init smp_prepare_cpus(unsigned int max_cpus) 
	if (vdso_alloc_per_cpu(smp_processor_id(), &S390_lowcore))

		BUG();

#endif

	for_each_possible_cpu(cpu)

		if (cpu != smp_processor_id())

			smp_create_idle(cpu);

}



void __init smp_prepare_boot_cpu(void)