Re: [PATCH 1/4] sched: move IO scheduling accounting from io_schedule_timeout() to __schedule()

Peter Zijlstra
2016-10-28T18:27:22Z

On Fri, Oct 28, 2016 at 12:58:09PM -0400, Tejun Heo wrote:
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3336,11 +3336,17 @@ static void __sched notrace __schedule(bool preempt)
> unsigned long *switch_count;
> struct pin_cookie cookie;
> struct rq *rq;
> - int cpu;
> + int cpu, in_iowait;
>
> cpu = smp_processor_id();
> rq = cpu_rq(cpu);
> prev = rq->curr;
> + in_iowait = prev->in_iowait;
> +
> + if (in_iowait) {
> + delayacct_blkio_start();
> + atomic_inc(&rq->nr_iowait);
> + }
>
> schedule_debug(prev);
>
> @@ -3406,6 +3412,11 @@ static void __sched notrace __schedule(bool preempt)
> }
>
> balance_callback(rq);
> +
> + if (in_iowait) {
> + atomic_dec(&rq->nr_iowait);
> + delayacct_blkio_end();
> + }
> }
>
> void __noreturn do_task_dead(void)

Urgh, can't say I like this much. It moves two branches into the
schedule path.

Nor do I really like the idea of having to annotate special mutexes for
the iowait crap.

I'll think more after KS/LPC etc..