linux-kernel - Re: [PATCH 6/7] psi: pressure stall information for CPU, memory, and IO

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Date:   Wed, 23 May 2018 09:17:47 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Vinayak Menon <vinmenon@...eaurora.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-block@...r.kernel.org, cgroups@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...uxfoundation.org>,
        Tejun Heo <tj@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Mike Galbraith <efault@....de>,
        Oliver Yang <yangoliver@...com>,
        Shakeel Butt <shakeelb@...gle.com>,
        xxx xxx <x.qendo@...il.com>,
        Taras Kondratiuk <takondra@...co.com>,
        Daniel Walker <danielwa@...co.com>,
        Ruslan Ruslichenko <rruslich@...co.com>, kernel-team@...com
Subject: Re: [PATCH 6/7] psi: pressure stall information for CPU, memory, and
 IO

On Wed, May 09, 2018 at 04:33:24PM +0530, Vinayak Menon wrote:
> On 5/8/2018 2:31 AM, Johannes Weiner wrote:
> > +	/* Kick the stats aggregation worker if it's gone to sleep */
> > +	if (!delayed_work_pending(&group->clock_work))
> 
> This causes a crash when the work is scheduled before system_wq is up. In my case when the first
> schedule was called from kthreadd. And I had to do this to make it work.
> if (keventd_up() && !delayed_work_pending(&group->clock_work))
>
> > +		schedule_delayed_work(&group->clock_work, MY_LOAD_FREQ);

I was trying to figure out how this is possible, and it didn't make
sense because we do initialize the system_wq way before kthreadd.

Did you by any chance backport this to a pre-4.10 kernel which does
not have 3347fa092821 ("workqueue: make workqueue available early
during boot") yet?

> > +void psi_task_change(struct task_struct *task, u64 now, int clear, int set)
> > +{
> > +	struct cgroup *cgroup, *parent;
> 
> unused variables

They're used in the next patch, I'll fix that up.

Thanks