From: Stan Hoeppner <stan@hardwarefreak.com>
To: xfs@oss.sgi.com
Subject: Re: How to track down abysmal performance ata - raid1 - crypto - vg/lv - xfs
Date: Sat, 07 Aug 2010 18:43:29 -0500 [thread overview]
Message-ID: <4C5DEFA1.4010506@hardwarefreak.com> (raw)
In-Reply-To: <20100807101349.GD7362@dastard>
Dave Chinner put forth on 8/7/2010 5:13 AM:
> On Thu, Aug 05, 2010 at 03:33:17AM -0500, Stan Hoeppner wrote:
>> Neil Brown put forth on 8/4/2010 5:24 PM:
>>
>>> Both page-cache and read-ahead work at the filesystem level
>>
>> Are you referring to /sys/block/sdx/queue/read_ahead_kb? I'm pretty sure this
>> works below the FS level and below the partition level. This read_ahead works
>> at the block device level. At least for individual or JBOD.
>
> That number is used to initialise the default readahead value for
> any file descriptor opened on the filesystem. readahead is tracked
> per-fd at the page cache level, so is effectively at the filesystem
> level, not the block device.
>
>> Are you saying this setting gets ignored by the kernel if/when mdadm, LVM,
>> and/or crypto are used?
>
> Only the value from the block device the filesystem sits on is used.
> i.e. if you are using /dev/md0, then the filesystem uses the value
> from /sys/block/md0/queue/read_ahead_kb and ignores all the ones set
> on the /dev/sdX devices that make up /dev/md0.
Thanks for the clarification/education Dave.
--
Stan
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next prev parent reply other threads:[~2010-08-07 23:40 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-08-04 7:35 How to track down abysmal performance ata - raid1 - crypto - vg/lv - xfs Dominik Brodowski
2010-08-04 8:50 ` Christoph Hellwig
2010-08-04 9:13 ` Dominik Brodowski
2010-08-04 9:21 ` Christoph Hellwig
2010-08-04 9:16 ` Michael Monnerie
2010-08-04 10:25 ` Dominik Brodowski
2010-08-04 11:18 ` Christoph Hellwig
2010-08-04 11:24 ` Dominik Brodowski
2010-08-04 11:53 ` Mikael Abrahamsson
2010-08-04 12:56 ` Mike Snitzer
2010-08-04 22:24 ` Neil Brown
2010-08-05 8:33 ` Stan Hoeppner
2010-08-07 10:13 ` Dave Chinner
2010-08-07 23:43 ` Stan Hoeppner [this message]
2010-08-08 7:46 ` Michael Monnerie
2010-08-04 20:33 ` Valdis.Kletnieks
2010-08-05 9:31 ` direct-io regression [Was: How to track down abysmal performance ata - raid1 - crypto - vg/lv - xfs] Dominik Brodowski
2010-08-05 11:32 ` Chris Mason
2010-08-05 12:36 ` Josef Bacik
2010-08-05 15:35 ` Dominik Brodowski
2010-08-05 15:39 ` Chris Mason
2010-08-05 15:53 ` Dominik Brodowski
2010-08-05 16:35 ` Dominik Brodowski
2010-08-05 20:47 ` Performance impact of CONFIG_DEBUG? direct-io test case Dominik Brodowski
2010-08-05 20:54 ` Performance impact of CONFIG_SCHED_MC? " Dominik Brodowski
2010-08-05 18:58 ` direct-io regression [Was: How to track down abysmal performance ata - raid1 - crypto - vg/lv - xfs] Jeff Moyer
2010-08-05 19:01 ` Chris Mason
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