linux-kernel - Re: [RFC v1] add new io-scheduler to use cgroup on high-speed device

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Date:	Tue, 4 Jun 2013 20:03:37 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Robin Dong <sanbai@...bao.com>
Cc:	linux-kernel@...r.kernel.org, Zhu Yanhai <gaoyang.zyh@...bao.com>,
	Vivek Goyal <vgoyal@...hat.com>, Jens Axboe <axboe@...nel.dk>,
	Tao Ma <taoma.tm@...il.com>, kent.overstreet@...il.com
Subject: Re: [RFC v1] add new io-scheduler to use cgroup on high-speed device

(cc'ing Kent.  Original posting at
 http://thread.gmane.org/gmane.linux.kernel/1502484 )

Hello,

On Wed, Jun 05, 2013 at 10:09:31AM +0800, Robin Dong wrote:
> We want to use blkio.cgroup on high-speed device (like fusionio) for our mysql clusters.
> After testing different io-scheduler, we found that  cfq is too slow and deadline can't run on cgroup.
> So we developed a new io-scheduler: tpps (Tiny Parallel Proportion Scheduler).It dispatch requests
> only by using their individual weight and total weight (proportion) therefore it's simply and efficient.
> 
> Test case: fusionio card, 4 cgroups, iodepth-512

So, while I understand the intention behind it, I'm not sure a
separate io-sched for this is what we want.  Kent and Jens have been
thinking about this lately so they'll probably chime in.  From my POV,
I see a few largish issues.

* It has to be scalable with relatively large scale SMP / NUMA
  configurations.  It better integrate with blk-mq support currently
  being brewed.

* It definitely has to support hierarchy.  Nothing which doesn't
  support full hierarchy can be added to cgroup at this point.

* We already have separate implementations in blk-throtl and
  cfq-iosched.  Maybe it's too late and too different for cfq-iosched
  given that it's primarily targeted at disks, but I wonder whether we
  can make blk-throtl generic and scalable enough to cover all other
  use cases.

Thanks.

-- 
tejun
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