what does nr_iowait_cpu() do?

[shhuiw]

Right.  I found the following code snippet:

3715 /*
3716  * This task is about to go to sleep on IO. Increment rq->nr_iowait so
3717  * that process accounting knows that this is a task in IO wait state.
3718  */
3719 void __sched io_schedule(void)
3720 {
3721         struct rq *rq = raw_rq();
3722
3723         delayacct_blkio_start();
3724         atomic_inc(&rq->nr_iowait);
3725         blk_flush_plug(current);
3726         current->in_iowait = 1;
3727         schedule();
3728         current->in_iowait = 0;
3729         atomic_dec(&rq->nr_iowait);
3730         delayacct_blkio_end();
3731 }
3732 EXPORT_SYMBOL(io_schedule);




--

Regards,
shhuiw




At 2014-07-15 10:28:57, "Mohammad Merajul Islam Molla" <meraj.enigma at gmail.com> wrote:
>Number of processes waiting for I/O to complete on a cpu?
>
>On Tue, Jul 15, 2014 at 8:22 AM, Andev <debiandev at gmail.com> wrote:
>> On Mon, Jul 14, 2014 at 10:21 PM, Mohammad Merajul Islam Molla
>> <meraj.enigma at gmail.com> wrote:
>>> Hi Andev,
>>>
>>> Thanks for reply. I got the definition too. What I really want to know
>>> is what this variable nr_iowait stands for?
>>> Is it counting pending input/output on a cpu?
>>>
>>>
>>> --
>>> - Meraj
>>>
>>>
>>>
>>> On Tue, Jul 15, 2014 at 8:07 AM, Andev <debiandev at gmail.com> wrote:
>>>> On Mon, Jul 14, 2014 at 10:10 AM, Mohammad Merajul Islam Molla
>>>> <meraj.enigma at gmail.com> wrote:
>>>>> Hello,
>>>>>
>>>>> I was looking into the code of cpuidle menu governor and it uses a
>>>>> function nr_iowait_cpu(int cpu).
>>>>> I could not find out what this function does.
>>>>>
>>>>> Can someone please explain what nr_iowait_cpu(int cpu) and variant
>>>>> nr_iowait() do?
>>>>>
>>>>> --
>>
>> Now that is a better question. Try looking up what nr_iowait is.
>>
>>>>
>>>> In all its glory:
>>>>
>>>> unsigned long nr_iowait_cpu(int cpu)
>>>> {
>>>>     struct rq *this = cpu_rq(cpu);
>>>>     return atomic_read(&this->nr_iowait);
>>>> }
>>>>
>>>>
>>>>> Thanks,
>>>>> -Meraj
>>>>>
>>>>> _______________________________________________
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>>>>
>>>>
>>>>
>>>> --
>>>> Andev
>>
>>
>>
>> --
>> Andev
>
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