Re: [PATCH v8 4/8] smp: add func to IPI cpus based on parameter func
From: Srivatsa S. Bhat <hidden>
Date: 2012-02-05 15:36:38
Also in:
linux-fsdevel, lkml
On 02/05/2012 07:18 PM, Gilad Ben-Yossef wrote:
Add the on_each_cpu_cond() function that wraps on_each_cpu_mask() and calculates the cpumask of cpus to IPI by calling a function supplied as a parameter in order to determine whether to IPI each specific cpu. The function works around allocation failure of cpumask variable in CONFIG_CPUMASK_OFFSTACK=y by itereating over cpus sending an IPI a time via smp_call_function_single(). The function is useful since it allows to seperate the specific code that decided in each case whether to IPI a specific cpu for a specific request from the common boilerplate code of handling creating the mask, handling failures etc. Signed-off-by: Gilad Ben-Yossef <gilad@benyossef.com>
...
quoted hunk ↗ jump to hunk
diff --git a/include/linux/smp.h b/include/linux/smp.h index d0adb78..da4d034 100644 --- a/include/linux/smp.h +++ b/include/linux/smp.h@@ -109,6 +109,15 @@ void on_each_cpu_mask(const struct cpumask *mask, smp_call_func_t func, void *info, bool wait); /* + * Call a function on each processor for which the supplied function + * cond_func returns a positive value. This may include the local + * processor. + */ +void on_each_cpu_cond(bool (*cond_func)(int cpu, void *info), + smp_call_func_t func, void *info, bool wait, + gfp_t gfp_flags); + +/* * Mark the boot cpu "online" so that it can call console drivers in * printk() and can access its per-cpu storage. */@@ -153,6 +162,21 @@ static inline int up_smp_call_function(smp_call_func_t func, void *info) local_irq_enable(); \ } \ } while (0) +/* + * Preemption is disabled here to make sure the + * cond_func is called under the same condtions in UP + * and SMP. + */ +#define on_each_cpu_cond(cond_func, func, info, wait, gfp_flags) \ + do { \ + preempt_disable(); \ + if (cond_func(0, info)) { \ + local_irq_disable(); \ + (func)(info); \ + local_irq_enable(); \ + } \ + preempt_enable(); \ + } while (0) static inline void smp_send_reschedule(int cpu) { } #define num_booting_cpus() 1diff --git a/kernel/smp.c b/kernel/smp.c index a081e6c..28cbcc5 100644 --- a/kernel/smp.c +++ b/kernel/smp.c@@ -730,3 +730,63 @@ void on_each_cpu_mask(const struct cpumask *mask, smp_call_func_t func, put_cpu(); } EXPORT_SYMBOL(on_each_cpu_mask); + +/* + * on_each_cpu_cond(): Call a function on each processor for which + * the supplied function cond_func returns true, optionally waiting + * for all the required CPUs to finish. This may include the local + * processor. + * @cond_func: A callback function that is passed a cpu id and + * the the info parameter. The function is called + * with preemption disabled. The function should + * return a blooean value indicating whether to IPI + * the specified CPU. + * @func: The function to run on all applicable CPUs. + * This must be fast and non-blocking. + * @info: An arbitrary pointer to pass to both functions. + * @wait: If true, wait (atomically) until function has + * completed on other CPUs. + * @gfp_flags: GFP flags to use when allocating the cpumask + * used internally by the function. + * + * The function might sleep if the GFP flags indicates a non + * atomic allocation is allowed. + * + * Preemption is disabled to protect against a hotplug event.
Well, disabling preemption protects us only against CPU offline right? (because we use the stop_machine thing during cpu offline). What about CPU online? Just to cross-check my understanding of the code with the existing documentation on CPU hotplug, I looked up Documentation/cpu-hotplug.txt and this is what I found: "If you merely need to avoid cpus going away, you could also use preempt_disable() and preempt_enable() for those sections.... ...The preempt_disable() will work as long as stop_machine_run() is used to take a cpu down." So even this only talks about using preempt_disable() to prevent CPU offline, not CPU online. Or, am I missing something?
+ *
+ * You must not call this function with disabled interrupts or
+ * from a hardware interrupt handler or from a bottom half handler.
+ */
+void on_each_cpu_cond(bool (*cond_func)(int cpu, void *info),
+ smp_call_func_t func, void *info, bool wait,
+ gfp_t gfp_flags)
+{
+ cpumask_var_t cpus;
+ int cpu, ret;
+
+ might_sleep_if(gfp_flags & __GFP_WAIT);
+
+ if (likely(zalloc_cpumask_var(&cpus, (gfp_flags|__GFP_NOWARN)))) {
+ preempt_disable();
+ for_each_online_cpu(cpu)
+ if (cond_func(cpu, info))
+ cpumask_set_cpu(cpu, cpus);IOW, what prevents a new CPU from becoming online at this point?
+ on_each_cpu_mask(cpus, func, info, wait);
+ preempt_enable();
+ free_cpumask_var(cpus);
+ } else {
+ /*
+ * No free cpumask, bother. No matter, we'll
+ * just have to IPI them one by one.
+ */
+ preempt_disable();
+ for_each_online_cpu(cpu)
+ if (cond_func(cpu, info)) {
+ ret = smp_call_function_single(cpu, func,
+ info, wait);
+ WARN_ON_ONCE(!ret);
+ }
+ preempt_enable();
+ }
+}
+EXPORT_SYMBOL(on_each_cpu_cond);Regards, Srivatsa S. Bhat -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>