Re: [PATCH 2/4] sched: Account per task_group nr_iowait

[Peter Zijlstra]

On Mon, Nov 06, 2017 at 05:40:32PM +0300, Kirill Tkhai wrote:
> The patch makes number of task_group's tasks in iowait state
> be tracked separately. This may be useful for containers to
> check nr_iowait state of a single one.
> 
> Signed-off-by: Kirill Tkhai <ktk...@virtuozzo.com>
> ---
>  kernel/sched/core.c  |   45 +++++++++++++++++++++++++++++++++++++++++++++
>  kernel/sched/sched.h |    5 +++++
>  2 files changed, 50 insertions(+)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 712ee54edaa1..86d1ad5f49bd 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -796,12 +796,32 @@ void deactivate_task(struct rq *rq, struct task_struct 
> *p, int flags)
>  
>  static void task_iowait_start(struct rq *rq, struct task_struct *p)
>  {
> +#ifdef CONFIG_CGROUP_SCHED
> +     struct task_group *tg = task_group(p);
> +
> +     /* Task's sched_task_group is changed under both of the below locks */
> +     BUG_ON(!raw_spin_is_locked(&p->pi_lock) && 
> !raw_spin_is_locked(&rq->lock));

We have lockdep_assert_held for that.

> +     while (task_group_is_autogroup(tg))
> +             tg = tg->parent;
> +     atomic_inc(&tg->stat[rq->cpu].nr_iowait);

You're joking right, more atomic ops on the fast paths..

> +#endif
> +
>       atomic_inc(&rq->nr_iowait);
>       delayacct_blkio_start();