diff mbox

[RFC,v3,9/9] cpu: No more __stop_machine() in _cpu_down()

Message ID 20121207174018.27305.63045.stgit@srivatsabhat.in.ibm.com (mailing list archive)
State RFC, archived
Headers show

Commit Message

Srivatsa S. Bhat Dec. 7, 2012, 5:40 p.m. UTC 
From: Paul E. McKenney <paul.mckenney@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_one_cpu() 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_atomic(), 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>
[ srivatsa.bhat@linux.vnet.ibm.com: Refer to the new sync primitives for
  readers (in the changelog), and s/stop_cpus/stop_one_cpu ]
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
---

 kernel/cpu.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)


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diff mbox

Patch

diff --git a/kernel/cpu.c b/kernel/cpu.c
index d2076fa..71c65dc 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -532,7 +532,7 @@  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_one_cpu(cpu, take_cpu_down, &tcd_param);
 	if (err) {
 		/* CPU didn't die: tell everyone.  Can't complain. */
 		smpboot_unpark_threads(cpu);