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From: Vivek Goyal <vgoyal@redhat.com>
To: Shaohua Li <shli@kernel.org>
Cc: Tao Ma <tm@tao.ma>, Tejun Heo <tj@kernel.org>,
	axboe@kernel.dk, ctalbott@google.com, rni@google.com,
	linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
	containers@lists.linux-foundation.org
Subject: Re: IOPS based scheduler (Was: Re: [PATCH 18/21] blkcg: move blkio_group_conf->weight to cfq)
Date: Wed, 4 Apr 2012 11:10:14 -0400	[thread overview]
Message-ID: <20120404151014.GD12676@redhat.com> (raw)
In-Reply-To: <CANejiEVD6nFVqX8Jf_hmRHg8YyBvPxbTVjgEif3mO1aa925KkQ@mail.gmail.com>

On Wed, Apr 04, 2012 at 07:52:24AM -0700, Shaohua Li wrote:

[..]
> Agreed, we can tweak cfq to make it support iops fairness because the two
> are conceptually the same. The problem is if this is a mess. CFQ is quite
> complicated already. In iops mode, a lot of code isn't required, like idle,
> queue merging, thinktime/seek detection and so on, as the scheduler
> will be only for ssd. With recent iocontext cleanup, the iops scheduler
> code is quite short actually.

Ok, this is somewhat a better reason to have a separate scheduler. I guess
we need to look that actual iops code and that can help decide whether
to keep it as a separate scheduler.

One question is still unanswered though. What real workload benefits
from it? If you are not doing idling in iops based scheduler, I doubt
you are doing to see much service differentiation on fast SSDs. As for
service differentiation IO queues have to be continuously backlogged and
total IOPS needed by applications need to be more than what disk can
offer. It becomes very hard to produe continuously backlogged queues
because real applications tend to read some data, proces data and then
generate more IO. 

Thanks
Vivek

  reply	other threads:[~2012-04-04 15:10 UTC|newest]

Thread overview: 56+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-03-28 22:51 [PATCHSET] block: modularize blkcg config and stat file handling Tejun Heo
2012-03-28 22:51 ` [PATCH 01/21] blkcg: remove unused @pol and @plid parameters Tejun Heo
2012-03-28 22:51 ` [PATCH 02/21] blkcg: BLKIO_STAT_CPU_SECTORS doesn't have subcounters Tejun Heo
2012-03-28 22:51 ` [PATCH 03/21] blkcg: introduce blkg_stat and blkg_rwstat Tejun Heo
2012-03-28 22:51 ` [PATCH 04/21] blkcg: restructure statistics printing Tejun Heo
2012-03-28 22:51 ` [PATCH 05/21] blkcg: drop blkiocg_file_write_u64() Tejun Heo
2012-03-28 22:51 ` [PATCH 06/21] blkcg: restructure configuration printing Tejun Heo
2012-03-28 22:51 ` [PATCH 07/21] blkcg: restructure blkio_group configruation setting Tejun Heo
2012-03-28 22:51 ` [PATCH 08/21] blkcg: blkg_conf_prep() Tejun Heo
2012-03-28 22:53   ` Tejun Heo
2012-03-28 22:51 ` [PATCH 09/21] blkcg: export conf/stat helpers to prepare for reorganization Tejun Heo
2012-03-28 22:51 ` [PATCH 10/21] blkcg: implement blkio_policy_type->cftypes Tejun Heo
2012-03-28 22:51 ` [PATCH 11/21] blkcg: move conf/stat file handling code to policies Tejun Heo
2012-03-28 22:51 ` [PATCH 12/21] cfq: collapse cfq.h into cfq-iosched.c Tejun Heo
2012-03-28 22:51 ` [PATCH 13/21] blkcg: move statistics update code to policies Tejun Heo
2012-03-28 22:51 ` [PATCH 14/21] blkcg: cfq doesn't need per-cpu dispatch stats Tejun Heo
2012-03-28 22:51 ` [PATCH 15/21] blkcg: add blkio_policy_ops operations for exit and stat reset Tejun Heo
2012-03-28 22:51 ` [PATCH 16/21] blkcg: move blkio_group_stats to cfq-iosched.c Tejun Heo
2012-03-28 22:51 ` [PATCH 17/21] blkcg: move blkio_group_stats_cpu and friends to blk-throttle.c Tejun Heo
2012-03-28 22:51 ` [PATCH 18/21] blkcg: move blkio_group_conf->weight to cfq Tejun Heo
2012-04-01 21:09   ` Vivek Goyal
2012-04-01 21:22     ` Tejun Heo
2012-04-02 21:39   ` Tao Ma
2012-04-02 21:49     ` Tejun Heo
2012-04-02 22:03       ` Tao Ma
2012-04-02 22:17         ` Tejun Heo
2012-04-02 22:20           ` Tao Ma
2012-04-02 22:25             ` Vivek Goyal
2012-04-02 22:28               ` Tejun Heo
2012-04-02 22:41               ` Tao Ma
2012-04-03 15:37                 ` IOPS based scheduler (Was: Re: [PATCH 18/21] blkcg: move blkio_group_conf->weight to cfq) Vivek Goyal
2012-04-03 16:36                   ` Tao Ma
2012-04-03 16:50                     ` Vivek Goyal
2012-04-03 17:26                       ` Tao Ma
2012-04-04 12:35                         ` Shaohua Li
2012-04-04 13:37                           ` Vivek Goyal
2012-04-04 14:52                             ` Shaohua Li
2012-04-04 15:10                               ` Vivek Goyal [this message]
2012-04-04 16:06                                 ` Tao Ma
2012-04-04 16:45                             ` Tao Ma
2012-04-04 16:50                               ` Vivek Goyal
2012-04-04 17:17                                 ` Vivek Goyal
2012-04-04 17:18                                 ` Tao Ma
2012-04-04 17:27                                   ` Vivek Goyal
2012-04-04 18:22                                   ` Vivek Goyal
2012-04-04 18:36                                     ` Tao Ma
2012-04-04 13:31                         ` Vivek Goyal
2012-03-28 22:51 ` [PATCH 19/21] blkcg: move blkio_group_conf->iops and ->bps to blk-throttle Tejun Heo
2012-03-28 22:51 ` [PATCH 20/21] blkcg: pass around pd->pdata instead of pd itself in prfill functions Tejun Heo
2012-03-28 22:51 ` [PATCH 21/21] blkcg: drop BLKCG_STAT_{PRIV|POL|OFF} macros Tejun Heo
2012-03-29  8:18 ` [PATCHSET] block: modularize blkcg config and stat file handling Jens Axboe
2012-04-02 20:02   ` Tejun Heo
2012-04-02 21:51     ` Jens Axboe
2012-04-02 22:33       ` Tejun Heo
2012-04-01 19:38 ` Vivek Goyal
2012-04-01 21:42 ` Tejun Heo

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