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 42bd331ee0abff1d542583e14beb20d91f6fae62..6b37ce0888d7a81e94589fc6af49fc88d59f87b8 100644 (file)
--- 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);