Commit 96498144 authored by James Hogan's avatar James Hogan
Browse files

metag: smp: don't spin waiting for CPU to start 



Use a completion to block until a secondary CPU has started up, like ARM
do, instead of a loop of udelays.

On Meta, SMP is really SMT, with each "CPU" being a different hardware
thread on the same Meta processor core, so as well as being more
efficient and latency friendly, using a completion prevents the bogomips
of the secondary CPU from being drastically skewed every time by the
execution of the tight in-cache udelay loop on the other CPU.

Signed-off-by: default avatarJames Hogan <james.hogan@imgtec.com>
Acked-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatar"Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
parent 234c7f1a

arch/metag/kernel/smp.c

+6 −10
Original line number Original line Diff line number Diff line
@@ -8,6 +8,7 @@ 
 * published by the Free Software Foundation.

 * published by the Free Software Foundation.

 */

 */

#include <linux/atomic.h>

#include <linux/atomic.h>

#include <linux/completion.h>

#include <linux/delay.h>

#include <linux/delay.h>

#include <linux/init.h>

#include <linux/init.h>

#include <linux/spinlock.h>

#include <linux/spinlock.h>
@@ -62,6 +63,8 @@ static DEFINE_PER_CPU(struct ipi_data, ipi_data) = { 




static DEFINE_SPINLOCK(boot_lock);

static DEFINE_SPINLOCK(boot_lock);





static DECLARE_COMPLETION(cpu_running);



/*

/*

 * "thread" is assumed to be a valid Meta hardware thread ID.

 * "thread" is assumed to be a valid Meta hardware thread ID.

 */

 */
@@ -235,20 +238,12 @@ int __cpuinit __cpu_up(unsigned int cpu, struct task_struct *idle) 
	 */

	 */

	ret = boot_secondary(thread, idle);

	ret = boot_secondary(thread, idle);

	if (ret == 0) {

	if (ret == 0) {

		unsigned long timeout;



		/*

		/*

		 * CPU was successfully started, wait for it

		 * CPU was successfully started, wait for it

		 * to come online or time out.

		 * to come online or time out.

		 */

		 */

		timeout = jiffies + HZ;

		wait_for_completion_timeout(&cpu_running,

		while (time_before(jiffies, timeout)) {

					    msecs_to_jiffies(1000));

			if (cpu_online(cpu))

				break;



			udelay(10);

			barrier();

		}





		if (!cpu_online(cpu))

		if (!cpu_online(cpu))

			ret = -EIO;

			ret = -EIO;
@@ -391,6 +386,7 @@ asmlinkage void secondary_start_kernel(void) 
	 * OK, now it's safe to let the boot CPU continue

	 * OK, now it's safe to let the boot CPU continue

	 */

	 */

	set_cpu_online(cpu, true);

	set_cpu_online(cpu, true);

	complete(&cpu_running);





	/*

	/*

	 * Enable local interrupts.

	 * Enable local interrupts.

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