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From: Ming Lei <ming.lei@redhat.com>
To: Yu Kuai <yukuai3@huawei.com>
Cc: axboe@kernel.dk, linux-block@vger.kernel.org,
	linux-kernel@vger.kernel.org, yi.zhang@huawei.com,
	zhangxiaoxu5@huawei.com
Subject: Re: [PATCH 1/3] blk-mq: allow hardware queue to get more tag while sharing a tag set
Date: Sun, 27 Dec 2020 19:58:59 +0800	[thread overview]
Message-ID: <20201227115859.GA3282759@T590> (raw)
In-Reply-To: <20201226102808.2534966-2-yukuai3@huawei.com>

Hi Yu Kuai,

On Sat, Dec 26, 2020 at 06:28:06PM +0800, Yu Kuai wrote:
> When sharing a tag set, if most disks are issuing small amount of IO, and
> only a few is issuing a large amount of IO. Current approach is to limit
> the max amount of tags a disk can get equally to the average of total
> tags. Thus the few heavy load disk can't get enough tags while many tags
> are still free in the tag set.

Yeah, current approach just allocates same share for each active queue
which is evaluated in each timeout period.

That said you are trying to improve the following case:
- heavy IO on one or several disks, and the average share for these
  disks become bottleneck of IO performance
- small amount IO on other disks attached to the same host, and all IOs are
submitted to disk in <30 second period.

Just wondering if you may share the workload you are trying to optimize,
or it is just one improvement in theory? And what is the disk(hdd, ssd
or nvme) and host? And how many disks in your setting? And how deep the tagset
depth is?


Thanks, 
Ming


  reply	other threads:[~2020-12-27 12:00 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-26 10:28 [PATCH 0/3] fix the performance fluctuation due to shared tagset Yu Kuai
2020-12-26 10:28 ` [PATCH 1/3] blk-mq: allow hardware queue to get more tag while sharing a tag set Yu Kuai
2020-12-27 11:58   ` Ming Lei [this message]
2020-12-28  1:56     ` yukuai (C)
2020-12-28  8:28       ` Ming Lei
2020-12-28  9:02         ` yukuai (C)
2020-12-29  1:15           ` Ming Lei
2020-12-29  2:37             ` yukuai (C)
2020-12-26 10:28 ` [PATCH 2/3] blk-mq: clear 'active_queues' immediately when 'nr_active' is decreased to 0 Yu Kuai
2020-12-26 10:28 ` [PATCH 3/3] blk-mq: decrease pending_queues when it expires Yu Kuai

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