Re: [PATCH] fs/dcache: resched/chill only if we make no progress

From: Thomas Gleixner
Date: Sat Sep 10 2016 - 02:19:44 EST


On Thu, 8 Sep 2016, Sebastian Andrzej Siewior wrote:
> + if (parent == dentry) {
> + /* the task with the highest priority won't schedule */
> + r = cond_resched();
> + if (!r && (rt_task(current) || dl_task(current)))

That's wrong because a non RT task will just spin until its time slice is
up. Wasted cycles for nothing.

Ideally we make spinning conditional on

!on_cpu(dentry->lock->owner)

That would avoid going to sleep if the owner runs on another cpu. We have
no mechanism for that, but I think it'd be worth to think about one.

> + cpu_chill();
> + } else
> + dentry = parent;

Missing braces

Thanks,

tglx