On Mon, Aug 8, 2011 at 8:25 PM, Jonathan Neuschäfer
<j.neuschaefer@xxxxxxx> 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
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