From f97f8f06a49febbc3cb3635172efbe64ddc79700 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Mon, 16 Jul 2012 10:42:36 +0000 Subject: smpboot: Provide infrastructure for percpu hotplug threads Provide a generic interface for setting up and tearing down percpu threads. On registration the threads for already online cpus are created and started. On deregistration (modules) the threads are stoppped. During hotplug operations the threads are created, started, parked and unparked. The datastructure for registration provides a pointer to percpu storage space and optional setup, cleanup, park, unpark functions. These functions are called when the thread state changes. Each implementation has to provide a function which is queried and returns whether the thread should run and the thread function itself. The core code handles all state transitions and avoids duplicated code in the call sites. [ paulmck: Preemption leak fix ] Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra Reviewed-by: Srivatsa S. Bhat Cc: Rusty Russell Reviewed-by: Paul E. McKenney Cc: Namhyung Kim Link: http://lkml.kernel.org/r/20120716103948.352501068@linutronix.de Signed-off-by: Thomas Gleixner --- kernel/cpu.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) (limited to 'kernel/cpu.c') diff --git a/kernel/cpu.c b/kernel/cpu.c index 14d32588cccd..e615dfbcf794 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -280,12 +280,13 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen) __func__, cpu); goto out_release; } + smpboot_park_threads(cpu); err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu)); if (err) { /* CPU didn't die: tell everyone. Can't complain. */ + smpboot_unpark_threads(cpu); cpu_notify_nofail(CPU_DOWN_FAILED | mod, hcpu); - goto out_release; } BUG_ON(cpu_online(cpu)); @@ -354,6 +355,10 @@ static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen) goto out; } + ret = smpboot_create_threads(cpu); + if (ret) + goto out; + ret = __cpu_notify(CPU_UP_PREPARE | mod, hcpu, -1, &nr_calls); if (ret) { nr_calls--; @@ -368,6 +373,9 @@ static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen) goto out_notify; BUG_ON(!cpu_online(cpu)); + /* Wake the per cpu threads */ + smpboot_unpark_threads(cpu); + /* Now call notifier in preparation. */ cpu_notify(CPU_ONLINE | mod, hcpu); -- cgit v1.2.3 From 816afe4ff98ee10b1d30fd66361be132a0a5cee6 Mon Sep 17 00:00:00 2001 From: Rusty Russell Date: Mon, 6 Aug 2012 17:29:49 +0930 Subject: x86/smp: Don't ever patch back to UP if we unplug cpus We still patch SMP instructions to UP variants if we boot with a single CPU, but not at any other time. In particular, not if we unplug CPUs to return to a single cpu. Paul McKenney points out: mean offline overhead is 6251/48=130.2 milliseconds. If I remove the alternatives_smp_switch() from the offline path [...] the mean offline overhead is 550/42=13.1 milliseconds Basically, we're never going to get those 120ms back, and the code is pretty messy. We get rid of: 1) The "smp-alt-once" boot option. It's actually "smp-alt-boot", the documentation is wrong. It's now the default. 2) The skip_smp_alternatives flag used by suspend. 3) arch_disable_nonboot_cpus_begin() and arch_disable_nonboot_cpus_end() which were only used to set this one flag. Signed-off-by: Rusty Russell Cc: Paul McKenney Cc: Suresh Siddha Cc: Linus Torvalds Cc: Andrew Morton Cc: Peter Zijlstra Link: http://lkml.kernel.org/r/87vcgwwive.fsf@rustcorp.com.au Signed-off-by: Ingo Molnar --- kernel/cpu.c | 11 ----------- 1 file changed, 11 deletions(-) (limited to 'kernel/cpu.c') diff --git a/kernel/cpu.c b/kernel/cpu.c index 14d32588cccd..f6bfe3e03f6b 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -439,14 +439,6 @@ EXPORT_SYMBOL_GPL(cpu_up); #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; @@ -458,7 +450,6 @@ 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) { @@ -474,8 +465,6 @@ 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 v1.2.3