linux-kernel - Re: [PATCH 08/10] blkcg: implement blk-iocost

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Message-ID: <20190829154609.GU2263813@devbig004.ftw2.facebook.com>
Date:   Thu, 29 Aug 2019 08:46:09 -0700
From:   Tejun Heo <tj@...nel.org>
To:     Hillf Danton <hdanton@...a.com>
Cc:     axboe@...nel.dk, newella@...com, clm@...com, josef@...icpanda.com,
        dennisz@...com, lizefan@...wei.com, hannes@...xchg.org,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        kernel-team@...com, cgroups@...r.kernel.org,
        Josef Bacik <jbacik@...com>, Rik van Riel <riel@...riel.com>
Subject: Re: [PATCH 08/10] blkcg: implement blk-iocost

Hello,

On Thu, Aug 29, 2019 at 09:39:28PM +0800, Hillf Danton wrote:
> > +	on_q_ns = ktime_get_ns() - rq->alloc_time_ns;
> > +	rq_wait_ns = rq->start_time_ns - rq->alloc_time_ns;
> > +
> ehm... alloc_time makes no sense wrt start_time if this is their only
> use. What are you trying to measure with the two stamps if they are
> meaningfully apart?

Queue depth depletion.

> > +	rq_qos_add(q, rqos);
> > +	ret = blkcg_activate_policy(q, &blkcg_policy_iocost);
> > +	if (ret) {
> > +		rq_qos_del(q, rqos);
> 
> 		free_percpu(ioc->pcpu_stat);

Good catch.  Will send a follow up patch.

Thanks.

-- 
tejun