| From | "Srivatsa S. Bhat" <> | Subject | [PATCH v5 43/45] cpu: No more __stop_machine() in _cpu_down() | Date | Tue, 22 Jan 2013 13:14:58 +0530 |
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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.
There were a number of uses of preempt_disable() or local_irq_disable() that were intended to block CPU-hotplug offlining. These were fixed by using get/put_online_cpus_atomic(), which is the new synchronization primitive to prevent CPU offline, while invoking from atomic context.
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); s/stop_cpus/stop_one_cpu and fix comment referring to stop_machine in the code] Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> ---
kernel/cpu.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/cpu.c b/kernel/cpu.c index 1c84138..7a51fb6 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -337,7 +337,7 @@ 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); @@ -349,7 +349,7 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen) /* * The migration_call() CPU_DYING callback will have removed all * runnable tasks from the cpu, there's only the idle task left now - * that the migration thread is done doing the stop_machine thing. + * that the migration thread is done doing the stop_one_cpu() thing. * * Wait for the stop thread to go away. */
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