b09caeac92
Introduce migrate_disable(). The task can't be pushed to another CPU but can be preempted. From: Peter Zijlstra <a.p.zijlstra@chello.nl>: |Make migrate_disable() be a preempt_disable() for !rt kernels. This |allows generic code to use it but still enforces that these code |sections stay relatively small. | |A preemptible migrate_disable() accessible for general use would allow |people growing arbitrary per-cpu crap instead of clean these things |up. From: Steven Rostedt <rostedt@goodmis.org> | The migrate_disable() can cause a bit of a overhead to the RT kernel, | as changing the affinity is expensive to do at every lock encountered. | As a running task can not migrate, the actual disabling of migration | does not need to occur until the task is about to schedule out. | | In most cases, a task that disables migration will enable it before | it schedules making this change improve performance tremendously. On top of this build get/put_cpu_light(). It is similar to get_cpu(): it uses migrate_disable() instead of preempt_disable(). That means the user remains on the same CPU but the function using it may be preempted and invoked again from another caller on the same CPU. Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
66 lines
1.4 KiB
C
66 lines
1.4 KiB
C
/*
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* lib/smp_processor_id.c
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*
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* DEBUG_PREEMPT variant of smp_processor_id().
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*/
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#include <linux/export.h>
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#include <linux/kallsyms.h>
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#include <linux/sched.h>
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notrace static unsigned int check_preemption_disabled(const char *what1,
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const char *what2)
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{
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int this_cpu = raw_smp_processor_id();
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if (likely(preempt_count()))
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goto out;
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if (irqs_disabled())
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goto out;
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/*
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* Kernel threads bound to a single CPU can safely use
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* smp_processor_id():
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*/
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if (cpumask_equal(tsk_cpus_allowed(current), cpumask_of(this_cpu)))
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goto out;
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/*
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* It is valid to assume CPU-locality during early bootup:
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*/
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if (system_state != SYSTEM_RUNNING)
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goto out;
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/*
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* Avoid recursion:
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*/
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preempt_disable_notrace();
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if (!printk_ratelimit())
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goto out_enable;
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printk(KERN_ERR "BUG: using %s%s() in preemptible [%08x %08x] code: %s/%d\n",
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what1, what2, preempt_count() - 1, __migrate_disabled(current),
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current->comm, current->pid);
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print_symbol("caller is %s\n", (long)__builtin_return_address(0));
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dump_stack();
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out_enable:
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preempt_enable_no_resched_notrace();
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out:
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return this_cpu;
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}
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notrace unsigned int debug_smp_processor_id(void)
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{
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return check_preemption_disabled("smp_processor_id", "");
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}
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EXPORT_SYMBOL(debug_smp_processor_id);
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notrace void __this_cpu_preempt_check(const char *op)
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{
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check_preemption_disabled("__this_cpu_", op);
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}
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EXPORT_SYMBOL(__this_cpu_preempt_check);
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