From 9649814432faa9016952895684120942da0d8481 Mon Sep 17 00:00:00 2001 From: James Hogan Date: Fri, 28 Jun 2013 15:03:05 +0100 Subject: [PATCH] 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: James Hogan Acked-by: Thomas Gleixner Reviewed-by: "Srivatsa S. Bhat" --- 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 +#include #include #include #include @@ -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. -- 2.7.4