From: Paul E. McKenney <paul.mckenney@linaro.org>
Date: Thu, 26 Jul 2012 17:55:55 +0000 (-0700)
Subject: cpu: No more __stop_machine() in _cpu_down()
X-Git-Tag: next-20121024~29^2~2^3~4
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=45a8e3df27070736bbe80af57df3d8c86e5cfdf3;p=karo-tx-linux.git

cpu: No more __stop_machine() in _cpu_down()

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, but in the meantime, this commit is one way to help
locate them.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 42bd331ee0ab..6b37ce0888d7 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -247,13 +247,18 @@ static int __ref take_cpu_down(void *_param)
 {
 	struct take_cpu_down_param *param = _param;
 	int err;
+	unsigned long flags;
 
 	/* 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;
 }
 
@@ -286,7 +291,7 @@ 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);