From: Paul E. McKenney <paul.mcken...@linaro.org>
The _cpu_down() function invoked as part of the CPU-hotplug offlining
process currently invokes __stop_machine(), which is slow and inflicts
substantial real-time latencies on the entire system. This patch
substitutes stop_cpus() for __stop_machine() in order to improve
both performance and real-time latency.
This is currently unsafe, because there are a number of uses of
preempt_disable() that are intended to block CPU-hotplug offlining.
These will be fixed by using get/put_online_cpus_stable_atomic(), but in the
meantime, this commit is one way to help locate them.
Signed-off-by: Paul E. McKenney <paul.mcken...@linaro.org>
Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
[ Srivatsa: Refer to get/put_online_cpus_stable_atomic() in the changelog ]
Signed-off-by: Srivatsa S. Bhat <srivatsa.b...@linux.vnet.ibm.com>
---
kernel/cpu.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/kernel/cpu.c b/kernel/cpu.c
index aaf2393..59592e5 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -352,15 +352,20 @@ static int __ref take_cpu_down(void *_param)
{
struct take_cpu_down_param *param = _param;
int err, cpu = (long)(param->hcpu);
+ unsigned long flags;
prepare_cpu_take_down(cpu);
/* Ensure this CPU doesn't handle any more interrupts. */
+ local_irq_save(flags);
err = __cpu_disable();
- if (err < 0)
+ if (err < 0) {
+ local_irq_restore(flags);
return err;
+ }
cpu_notify(CPU_DYING | param->mod, param->hcpu);
+ local_irq_restore(flags);
return 0;
}
@@ -393,7 +398,7 @@ static int __ref _cpu_down(unsigned int cpu, int
tasks_frozen)
}
smpboot_park_threads(cpu);
- err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
+ err = stop_cpus(cpumask_of(cpu), take_cpu_down, &tcd_param);
if (err) {
/* CPU didn't die: tell everyone. Can't complain. */
smpboot_unpark_threads(cpu);
--
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