From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Srivatsa S. Bhat" Subject: [RFC PATCH v4 9/9] cpu: No more __stop_machine() in _cpu_down() Date: Tue, 11 Dec 2012 19:35:47 +0530 Message-ID: <20121211140541.23621.72514.stgit@srivatsabhat.in.ibm.com> References: <20121211140314.23621.64088.stgit@srivatsabhat.in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20121211140314.23621.64088.stgit@srivatsabhat.in.ibm.com> Sender: linux-kernel-owner@vger.kernel.org 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, tj@kernel.org, oleg@redhat.com Cc: sbw@mit.edu, 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 List-Id: linux-pm@vger.kernel.org From: Paul E. McKenney 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 Signed-off-by: Paul E. McKenney [ 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 --- kernel/cpu.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/cpu.c b/kernel/cpu.c index 5a63296..3f9498e 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -484,7 +484,7 @@ 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);