From: Wu Fengguang <wfg@linux.intel.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>, Jens Axboe <axboe@kernel.dk>,
Tejun Heo <tj@kernel.org>, Li Shaohua <shaohua.li@intel.com>,
Herbert Poetzl <herbert@13thfloor.at>
Subject: Re: Bad SSD performance with recent kernels
Date: Mon, 30 Jan 2012 22:05:38 +0800 [thread overview]
Message-ID: <20120130140537.GA20349@localhost> (raw)
In-Reply-To: <20120130140109.GA15682@localhost>
> - IO size is 256KB (which is not a problem in itself)
>
> - The dispatch/complete pattern is
>
> submit IO for range 1
> complete IO for range 1
> <dd busy, disk idle>
> submit IO for range 2
> complete IO for range 2
>
> So we have periods that no IO is in flight at all, which leads to
> under-utilized disk (which should show up in iostat as <100% disk util)
>
> # grep '[DC]' blktrace
>
> 8,16 1 770606 9.990039807 4580 D R 4379392 + 512 ( 14826) [dd]
> 8,16 1 770607 9.991083069 0 C R 4379392 + 512 ( 1043262) [0]
>
> 8,16 1 770739 9.991647434 4580 D R 4379904 + 512 ( 14433) [dd]
> 8,16 1 770740 9.992693317 0 C R 4379904 + 512 ( 1045883) [0]
>
> 8,16 1 770872 9.993256451 4580 D R 4380416 + 512 ( 14539) [dd]
> 8,16 1 770873 9.994299156 0 C R 4380416 + 512 ( 1042705) [0]
>
> 8,16 1 771005 9.994863680 4580 D R 4380928 + 512 ( 14344) [dd]
> 8,16 1 771006 9.995909291 0 C R 4380928 + 512 ( 1045611) [0]
>
> 8,16 1 771138 9.996470460 4580 D R 4381440 + 512 ( 14043) [dd]
> 8,16 1 771139 9.997514205 0 C R 4381440 + 512 ( 1043745) [0]
>
> 8,16 1 771271 9.998077269 4580 D R 4381952 + 512 ( 14928) [dd]
> 8,16 1 771272 9.999120396 0 C R 4381952 + 512 ( 1043127) [0]
Some better pattern for comparison:
8,0 1 42940 0.990199812 4084 D R 1432808 + 256 [dd]
8,0 1 42941 0.990858326 0 C R 1432552 + 256 [0]
8,0 1 43009 0.991192107 4084 D R 1433064 + 256 [dd]
8,0 3 14691 0.991853319 0 C R 1432808 + 256 [0]
8,0 3 14759 0.992189451 4084 D R 1433320 + 256 [dd]
8,0 1 43010 0.994473159 0 C R 1433064 + 256 [0]
Where the life time for requests 1432808, 1432552, 1433064, ...
are *interleaved* so that the disk always has something to do.
Thanks,
Fengguang
next prev parent reply other threads:[~2012-01-30 14:15 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-27 6:00 Bad SSD performance with recent kernels Herbert Poetzl
2012-01-27 6:44 ` Eric Dumazet
2012-01-28 12:51 ` Wu Fengguang
2012-01-28 13:33 ` Eric Dumazet
2012-01-29 5:59 ` Wu Fengguang
2012-01-29 8:42 ` Herbert Poetzl
2012-01-29 9:28 ` Wu Fengguang
2012-01-29 10:03 ` Eric Dumazet
2012-01-29 11:16 ` Wu Fengguang
2012-01-29 13:13 ` Eric Dumazet
2012-01-29 15:52 ` Pádraig Brady
2012-01-29 16:10 ` Wu Fengguang
2012-01-29 20:15 ` Herbert Poetzl
2012-01-30 11:18 ` Wu Fengguang
2012-01-30 12:34 ` Eric Dumazet
2012-01-30 14:01 ` Wu Fengguang
2012-01-30 14:05 ` Wu Fengguang [this message]
2012-01-30 3:17 ` Shaohua Li
2012-01-30 5:31 ` Eric Dumazet
2012-01-30 5:45 ` Shaohua Li
2012-01-30 7:13 ` Herbert Poetzl
2012-01-30 7:22 ` Shaohua Li
2012-01-30 7:36 ` Herbert Poetzl
2012-01-30 8:12 ` Shaohua Li
2012-01-30 10:31 ` Shaohua Li
2012-01-30 14:28 ` Wu Fengguang
2012-01-30 14:51 ` Eric Dumazet
2012-01-30 22:26 ` Vivek Goyal
2012-01-31 0:14 ` Shaohua Li
2012-01-31 1:07 ` Wu Fengguang
2012-01-31 3:00 ` Shaohua Li
2012-01-31 2:17 ` Eric Dumazet
2012-01-31 8:46 ` Eric Dumazet
2012-01-31 6:36 ` Herbert Poetzl
2012-01-30 14:48 ` Wu Fengguang
2012-01-28 17:01 ` Herbert Poetzl
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