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SubjectRe: [PATCH 2/4] sched: Account per task_group nr_iowait
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 <ktkhai@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();

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