From: Vivek Goyal <vgoyal@redhat.com>
To: Tejun Heo <tj@kernel.org>
Cc: lizefan@huawei.com, axboe@kernel.dk,
containers@lists.linux-foundation.org, cgroups@vger.kernel.org,
linux-kernel@vger.kernel.org, ctalbott@google.com,
rni@google.com
Subject: Re: [PATCH 07/12] cfq-iosched: implement hierarchy-ready cfq_group charge scaling
Date: Mon, 17 Dec 2012 16:49:11 -0500 [thread overview]
Message-ID: <20121217214911.GC13691@redhat.com> (raw)
In-Reply-To: <20121217213314.GF1844@htj.dyndns.org>
On Mon, Dec 17, 2012 at 01:33:14PM -0800, Tejun Heo wrote:
> Hello,
>
> On Mon, Dec 17, 2012 at 04:27:36PM -0500, Vivek Goyal wrote:
> > What I do care about is atleast being able to read and understand the
> > code easily. Right now, it is hard to understand. I am still struggling
> > to wrap my head around it.
>
> Hmm... I thought it was really simple. Maybe I'm just too familiar
> with it. You just walk up the tree multiplying the fraction you have
> at each level. It really doesn't get much simpler than that.
>
> > For example, while adding a group to service tree we calculate
> > cfqg->vfaction as follows.
> >
> > vfr = vfr * pos->leaf_weight / pos->level_weight;
> >
> > and then
> >
> > vfr = vfr * pos->weight / parent->level_weight;
> >
> > cfqg->vfraction = max_t(unsigned, vfr, 1)
> >
> > If cfqg->vfraction is about cfqg then why should we take into account
> > leaf_weight and level_weight. We should be just worried about pos->weight
> > and parent->level_weight and that should determine vfaction of cfqg.
>
> Eh? Then how would it compete with the children cfqgs? You can
> consider it as the hidden leaf node competing with the children cfqgs,
> right? So, you take the leaf weight and divide it by the total active
> weight of all the children (including the hidden leaf node). It isn't
> different from the rest of the calculation. It just looks different
> because leaf_weight is stored elsewhere and we look down there and
> then walke up. The calculation being done is exactly the same one.
Again it is coming from multiplexing cfqg and cfqg->task_group. So
effectively we are calculating the vfraction of task_group inside cfqg.
Once you say cfqg->vfraction, I immediately think of total share of
group (including task_group and all children cgroups).
May be cfqg->task_group_vfraction (or cfqg->tg_fraction) is a better name.
Also descrition says.
/* vfraction the fraction of vdisktime that a cfqg is entitled to */
May be we can clarify it that it is share of task_group of cfqg.
I guess i am too familiar with how cpu has done it. I think I am getting
confused with properties which belong to cfqg and properties which
belong to cfqg->task_group.
I guess if we prefix fields belong to task_group with somete suitable
string, it might become little easier to understand.
Thanks
Vivek
next prev parent reply other threads:[~2012-12-17 21:49 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-14 22:41 [PATCHSET] block: implement blkcg hierarchy support in cfq Tejun Heo
2012-12-14 22:41 ` [PATCH 01/12] blkcg: fix minor bug in blkg_alloc() Tejun Heo
2012-12-17 19:10 ` Vivek Goyal
2012-12-14 22:41 ` [PATCH 02/12] blkcg: reorganize blkg_lookup_create() and friends Tejun Heo
2012-12-17 19:28 ` Vivek Goyal
2012-12-14 22:41 ` [PATCH 03/12] blkcg: cosmetic updates to blkg_create() Tejun Heo
2012-12-17 19:37 ` Vivek Goyal
2012-12-14 22:41 ` [PATCH 04/12] blkcg: make blkcg_gq's hierarchical Tejun Heo
2012-12-17 20:04 ` Vivek Goyal
2012-12-14 22:41 ` [PATCH 05/12] cfq-iosched: add leaf_weight Tejun Heo
2012-12-14 22:41 ` [PATCH 06/12] cfq-iosched: implement cfq_group->nr_active and ->level_weight Tejun Heo
2012-12-17 20:46 ` Vivek Goyal
2012-12-17 21:15 ` Tejun Heo
2012-12-17 21:18 ` Vivek Goyal
2012-12-17 21:20 ` Tejun Heo
2012-12-14 22:41 ` [PATCH 07/12] cfq-iosched: implement hierarchy-ready cfq_group charge scaling Tejun Heo
2012-12-17 20:53 ` Vivek Goyal
2012-12-17 21:17 ` Tejun Heo
2012-12-17 21:27 ` Vivek Goyal
2012-12-17 21:33 ` Tejun Heo
2012-12-17 21:49 ` Vivek Goyal [this message]
2012-12-17 22:12 ` Tejun Heo
2012-12-14 22:41 ` [PATCH 08/12] cfq-iosched: convert cfq_group_slice() to use cfqg->vfraction Tejun Heo
2012-12-14 22:41 ` [PATCH 09/12] cfq-iosched: enable full blkcg hierarchy support Tejun Heo
2012-12-18 18:40 ` Vivek Goyal
2012-12-18 19:10 ` Tejun Heo
2012-12-18 19:16 ` Vivek Goyal
2012-12-18 19:17 ` Tejun Heo
2012-12-14 22:41 ` [PATCH 10/12] blkcg: add blkg_policy_data->plid Tejun Heo
2012-12-14 22:41 ` [PATCH 11/12] blkcg: implement blkg_prfill_[rw]stat_recursive() Tejun Heo
2012-12-14 22:41 ` [PATCH 12/12] cfq-iosched: add hierarchical cfq_group statistics Tejun Heo
2012-12-18 19:11 ` Vivek Goyal
2012-12-18 19:14 ` Tejun Heo
2012-12-18 19:18 ` Vivek Goyal
2012-12-18 19:21 ` Tejun Heo
2012-12-18 19:26 ` Vivek Goyal
2012-12-17 16:52 ` [PATCHSET] block: implement blkcg hierarchy support in cfq Vivek Goyal
2012-12-17 17:38 ` Tejun Heo
2012-12-17 18:50 ` Vivek Goyal
2012-12-17 18:59 ` Tejun Heo
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