difference between io_schedule() and schedule()

[Rajat Sharma]

On Mon, Aug 8, 2011 at 8:25 PM, Jonathan Neuschäfer
<j.neuschaefer at gmx.net> wrote:
> On Sat, Aug 06, 2011 at 12:31:21PM +0530, Rajat Sharma wrote:
>> Hi All,
>>
>> What is the difference between io_schedule() and schedule(), is
>> io_schedule() more restrictive to shedule only I/O bound processes or
>> it just favours I/O bound processes. Any documentation link would be
>> great help.
>
> Have you even looked at the source code?
>
> From kernel/sched.c +5721:
> /*
>  * This task is about to go to sleep on IO. Increment rq->nr_iowait so
>  * that process accounting knows that this is a task in IO wait state.
>  */
> void __sched io_schedule(void)
> {
>        struct rq *rq = raw_rq();
>
>        delayacct_blkio_start();
>        atomic_inc(&rq->nr_iowait);
>        blk_flush_plug(current);
>        current->in_iowait = 1;
>        schedule();
>        current->in_iowait = 0;
>        atomic_dec(&rq->nr_iowait);
>        delayacct_blkio_end();
> }
> EXPORT_SYMBOL(io_schedule);
>
> HTH,
>        Jonathan Neuschäfer
>

of course I looked at the source (obvious first step) before asking
question and further following tsk->in_iowait, it seems it is just
needed for accounting purpose.

                        if (tsk->in_iowait) {
                                se->statistics.iowait_sum += delta;
                                se->statistics.iowait_count++;
                                trace_sched_stat_iowait(tsk, delta);
                        }

Wanted to be sure of "is that it all about"? or I am missing something here?

-Rajat