From: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
To: tglx@linutronix.de, peterz@infradead.org,
paulmck@linux.vnet.ibm.com, rusty@rustcorp.com.au,
mingo@kernel.org, akpm@linux-foundation.org, namhyung@kernel.org,
vincent.guittot@linaro.org
Cc: sbw@mit.edu, tj@kernel.org, amit.kucheria@linaro.org,
rostedt@goodmis.org, rjw@sisk.pl,
srivatsa.bhat@linux.vnet.ibm.com, wangyun@linux.vnet.ibm.com,
xiaoguangrong@linux.vnet.ibm.com, nikunj@linux.vnet.ibm.com,
linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [RFC PATCH 10/10] cpu: No more __stop_machine() in _cpu_down()
Date: Tue, 04 Dec 2012 14:26:21 +0530 [thread overview]
Message-ID: <20121204085615.25919.98054.stgit@srivatsabhat.in.ibm.com> (raw)
In-Reply-To: <20121204085149.25919.29920.stgit@srivatsabhat.in.ibm.com>
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_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.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ Srivatsa: Refer to get/put_online_cpus_stable_atomic() in the changelog ]
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@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);
prev parent reply other threads:[~2012-12-04 8:57 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-04 8:53 [RFC PATCH 00/10] CPU hotplug: stop_machine()-free CPU hotplug Srivatsa S. Bhat
2012-12-04 8:53 ` [RFC PATCH 01/10] CPU hotplug: Introduce "stable" cpu online mask, for atomic hotplug readers Srivatsa S. Bhat
2012-12-04 15:17 ` Tejun Heo
2012-12-04 21:14 ` Srivatsa S. Bhat
2012-12-04 22:10 ` Andrew Morton
2012-12-05 2:56 ` Michael Wang
2012-12-05 3:28 ` Michael Wang
2012-12-05 12:38 ` Srivatsa S. Bhat
2012-12-04 8:54 ` [RFC PATCH 02/10] smp, cpu hotplug: Fix smp_call_function_*() to prevent CPU offline properly Srivatsa S. Bhat
2012-12-04 22:17 ` Andrew Morton
2012-12-05 12:41 ` Srivatsa S. Bhat
2012-12-04 23:39 ` Rusty Russell
2012-12-05 12:44 ` Srivatsa S. Bhat
2012-12-04 8:54 ` [RFC PATCH 03/10] smp, cpu hotplug: Fix on_each_cpu_*() " Srivatsa S. Bhat
2012-12-04 8:54 ` [RFC PATCH 04/10] sched, cpu hotplug: Use stable online cpus in try_to_wake_up() & select_task_rq() Srivatsa S. Bhat
2012-12-04 8:55 ` [RFC PATCH 05/10] kick_process(), cpu-hotplug: Prevent offlining of target CPU properly Srivatsa S. Bhat
2012-12-04 8:55 ` [RFC PATCH 06/10] yield_to(), cpu-hotplug: Prevent offlining of other CPUs properly Srivatsa S. Bhat
2012-12-04 8:55 ` [RFC PATCH 07/10] KVM: VMX: fix invalid cpu passed to smp_call_function_single Srivatsa S. Bhat
2012-12-04 8:55 ` [RFC PATCH 08/10] KVM: VMX: fix memory order between loading vmcs and clearing vmcs Srivatsa S. Bhat
2012-12-04 8:56 ` [RFC PATCH 09/10] KVM: VMX: fix unsyc vmcs status when cpu is going down Srivatsa S. Bhat
2012-12-04 8:56 ` Srivatsa S. Bhat [this message]
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