Messages in this thread | | | Date | Tue, 02 Jul 2013 11:42:39 +0530 | From | "Srivatsa S. Bhat" <> | Subject | Re: [PATCH 3/5] metag: smp: don't spin waiting for CPU to start |
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On 07/01/2013 09:34 PM, James Hogan wrote: > 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> > Cc: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com> > Cc: Thomas Gleixner <tglx@linutronix.de> > ---
Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Regards, 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 <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. >
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