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.ho...@imgtec.com>
Cc: "Srivatsa S. Bhat" <srivatsa.b...@linux.vnet.ibm.com>
Cc: Thomas Gleixner <t...@linutronix.de>
---
arch/metag/kernel/smp.c | 16 ++++++----------
1 file changed, 6 insertions(+), 10 deletions(-)
diff --git a/arch/metag/kernel/smp.c b/arch/metag/kernel/smp.c
index 09979f2..e413875 100644
--- a/arch/metag/kernel/smp.c
+++ b/arch/metag/kernel/smp.c
@@ -8,6 +8,7 @@
* published by the Free Software Foundation.
*/
#include <linux/atomic.h>
+#include <linux/completion.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/spinlock.h>
@@ -62,6 +63,8 @@ static DEFINE_PER_CPU(struct ipi_data, ipi_data) = {
static DEFINE_SPINLOCK(boot_lock);
+static DECLARE_COMPLETION(cpu_running);
+
/*
* "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);
if (ret == 0) {
- unsigned long timeout;
-
/*
* CPU was successfully started, wait for it
* to come online or time out.
*/
- timeout = jiffies + HZ;
- while (time_before(jiffies, timeout)) {
- if (cpu_online(cpu))
- break;
-
- udelay(10);
- barrier();
- }
+ wait_for_completion_timeout(&cpu_running,
+ msecs_to_jiffies(1000));
if (!cpu_online(cpu))
ret = -EIO;
@@ -391,6 +386,7 @@ asmlinkage void secondary_start_kernel(void)
* OK, now it's safe to let the boot CPU continue
*/
set_cpu_online(cpu, true);
+ complete(&cpu_running);
/*
* Enable local interrupts.
--
1.8.1.2
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
