From 48c5ccae88dcd989d9de507e8510313c6cbd352b Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Sat, 13 Nov 2010 19:32:29 +0100 Subject: sched: Simplify cpu-hot-unplug task migration While discussing the need for sched_idle_next(), Oleg remarked that since try_to_wake_up() ensures sleeping tasks will end up running on a sane cpu, we can do away with migrate_live_tasks(). If we then extend the existing hack of migrating current from CPU_DYING to migrating the full rq worth of tasks from CPU_DYING, the need for the sched_idle_next() abomination disappears as well, since idle will be the only possible thread left after the migration thread stops. This greatly simplifies the hot-unplug task migration path, as can be seen from the resulting code reduction (and about half the new lines are comments). Suggested-by: Oleg Nesterov Signed-off-by: Peter Zijlstra LKML-Reference: <1289851597.2109.547.camel@laptop> Signed-off-by: Ingo Molnar --- kernel/cpu.c | 16 ++++++---------- 1 file changed, 6 insertions(+), 10 deletions(-) (limited to 'kernel/cpu.c') diff --git a/kernel/cpu.c b/kernel/cpu.c index f6e726f18491..8615aa65d927 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -189,7 +189,6 @@ static inline void check_for_tasks(int cpu) } struct take_cpu_down_param { - struct task_struct *caller; unsigned long mod; void *hcpu; }; @@ -208,11 +207,6 @@ static int __ref take_cpu_down(void *_param) cpu_notify(CPU_DYING | param->mod, param->hcpu); - if (task_cpu(param->caller) == cpu) - move_task_off_dead_cpu(cpu, param->caller); - /* Force idle task to run as soon as we yield: it should - immediately notice cpu is offline and die quickly. */ - sched_idle_next(); return 0; } @@ -223,7 +217,6 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen) void *hcpu = (void *)(long)cpu; unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0; struct take_cpu_down_param tcd_param = { - .caller = current, .mod = mod, .hcpu = hcpu, }; @@ -253,9 +246,12 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen) } BUG_ON(cpu_online(cpu)); - /* Wait for it to sleep (leaving idle task). */ - while (!idle_cpu(cpu)) - yield(); + /* + * 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. + */ + BUG_ON(!idle_cpu(cpu)); /* This actually kills the CPU. */ __cpu_die(cpu); -- cgit v1.2.2 From 2e01f4740a874b6085da6ebf541e7ffde9a72bf2 Mon Sep 17 00:00:00 2001 From: Dhaval Giani Date: Thu, 18 Nov 2010 15:44:54 +0100 Subject: cpu: Remove unused variable MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit GCC warns us about: kernel/cpu.c: In function ‘take_cpu_down’: kernel/cpu.c:200:15: warning: unused variable ‘cpu’ This variable is unused since param->hcpu is directly used later on in cpu_notify. Signed-off-by: Dhaval Giani Signed-off-by: Peter Zijlstra LKML-Reference: <1290091494.1145.5.camel@gondor.retis> Signed-off-by: Ingo Molnar --- kernel/cpu.c | 1 - 1 file changed, 1 deletion(-) (limited to 'kernel/cpu.c') diff --git a/kernel/cpu.c b/kernel/cpu.c index 8615aa65d927..3945066fc01d 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -197,7 +197,6 @@ struct take_cpu_down_param { static int __ref take_cpu_down(void *_param) { struct take_cpu_down_param *param = _param; - unsigned int cpu = (unsigned long)param->hcpu; int err; /* Ensure this CPU doesn't handle any more interrupts. */ -- cgit v1.2.2 From 51a96c77815e7f139892a6e9c8275a50e9baebdf Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Fri, 19 Nov 2010 20:37:53 +0100 Subject: cpu: Remove incorrect BUG_ON Oleg mentioned that there is no actual guarantee the dying cpu's migration thread is actually finished running when we get there, so replace the BUG_ON() with a spinloop waiting for it. Reported-by: Oleg Nesterov Signed-off-by: Peter Zijlstra LKML-Reference: Signed-off-by: Ingo Molnar --- kernel/cpu.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) (limited to 'kernel/cpu.c') diff --git a/kernel/cpu.c b/kernel/cpu.c index 3945066fc01d..cb7a1efa9c2b 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -249,8 +249,11 @@ 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. + * + * Wait for the stop thread to go away. */ - BUG_ON(!idle_cpu(cpu)); + while (!idle_cpu(cpu)) + cpu_relax(); /* This actually kills the CPU. */ __cpu_die(cpu); -- cgit v1.2.2 From 3fb82d56ad003e804923185316236f26b30dfdd5 Mon Sep 17 00:00:00 2001 From: Suresh Siddha Date: Tue, 23 Nov 2010 16:11:40 -0800 Subject: x86, suspend: Avoid unnecessary smp alternatives switch during suspend/resume During suspend, we disable all the non boot cpus. And during resume we bring them all back again. So no need to do alternatives_smp_switch() in between. On my core 2 based laptop, this speeds up the suspend path by 15msec and the resume path by 5 msec (suspend/resume speed up differences can be attributed to the different P-states that the cpu is in during suspend/resume). Signed-off-by: Suresh Siddha LKML-Reference: <1290557500.4946.8.camel@sbsiddha-MOBL3.sc.intel.com> Cc: Rafael J. Wysocki Signed-off-by: H. Peter Anvin --- kernel/cpu.c | 11 +++++++++++ 1 file changed, 11 insertions(+) (limited to 'kernel/cpu.c') diff --git a/kernel/cpu.c b/kernel/cpu.c index f6e726f18491..8ccc182069ec 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -386,6 +386,14 @@ out: #ifdef CONFIG_PM_SLEEP_SMP static cpumask_var_t frozen_cpus; +void __weak arch_disable_nonboot_cpus_begin(void) +{ +} + +void __weak arch_disable_nonboot_cpus_end(void) +{ +} + int disable_nonboot_cpus(void) { int cpu, first_cpu, error = 0; @@ -397,6 +405,7 @@ int disable_nonboot_cpus(void) * with the userspace trying to use the CPU hotplug at the same time */ cpumask_clear(frozen_cpus); + arch_disable_nonboot_cpus_begin(); printk("Disabling non-boot CPUs ...\n"); for_each_online_cpu(cpu) { @@ -412,6 +421,8 @@ int disable_nonboot_cpus(void) } } + arch_disable_nonboot_cpus_end(); + if (!error) { BUG_ON(num_online_cpus() > 1); /* Make sure the CPUs won't be enabled by someone else */ -- cgit v1.2.2