difference between io_schedule() and schedule()

On Mon, Aug 8, 2011 at 8:25 PM, Jonathan Neusch?fer
[off-list ref] wrote:

On Sat, Aug 06, 2011 at 12:31:21PM +0530, Rajat Sharma wrote:

quoted

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 Neusch?fer

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