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

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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: James Hogan <james.hogan@imgtec.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
This commit is contained in:
James Hogan 2013-06-28 15:03:05 +01:00
parent 234c7f1ac1
commit 9649814432
1 changed files with 6 additions and 10 deletions
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16
arch/metag/kernel/smp.c
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@ -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.