On Mon, 9 Sep 2013 09:21:42 -0400 Steven Rostedt <rost...@goodmis.org> wrote:
> Especially since the function name itself is "rcu_is_cpu_idle()" which > tells you it's a cpu state, and not a task state. Why would you care in > RCU if CPU 1 is idle if you are on CPU 2? The name should be changed. > Actually, preempt_count is more a CPU state than a task state. When > preempt_count is set, that CPU can not schedule out the current task. > It really has nothing to do with the task itself. It's the CPU that > can't do something. Preempt count should never traverse with a task > from one CPU to another. I'll take this a step further. Here's a simple rule to determine if something is a task state or a CPU state. If the state migrates with a task from one CPU to another, it's a task state. If the state never leaves a CPU with a task, then it's a CPU state. According to the above rules, rcu_is_cpu_idle() is a task state, and really should be in task_struct, and preempt_count is a CPU state, and should be a per_cpu variable. I think the reason preempt_count never was a per cpu variable, is that having it in the stack (thread info) made it easier to test in assembly than having to grab the per cpu info. But I believe it's easier to grab per cpu info in assembly today than it once was, which is why there is a push to move preempt_count to per_cpu where it truly belongs. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
