From: Bernd Schubert <bernd.schubert@fastmail.fm>
To: Steven Haigh <netwiz@crc.id.au>
Cc: stan@hardwarefreak.com, linux-raid@vger.kernel.org
Subject: Re: Speeding up chunk size change?
Date: Sun, 04 Mar 2012 03:37:25 +0100 [thread overview]
Message-ID: <4F52D565.7040604@fastmail.fm> (raw)
In-Reply-To: <4F52D320.4080206@crc.id.au>
On 03/04/2012 03:27 AM, Steven Haigh wrote:
> On 4/03/2012 1:24 PM, Stan Hoeppner wrote:
>> On 3/3/2012 6:56 PM, Steven Haigh wrote:
>>> On 4/03/2012 8:42 AM, Stan Hoeppner wrote:
>> [snip]
>>>>> blockdev --setra 8192 /dev/sd[abcdefg]
>>>>
>>>> Read-ahead is per file descriptor, and occurs at the filesystem level.
>>>> The read-ahead value used is that of the device immediately underlying
>>>> the filessytem. So don't bother setting these above.
>>>
>>> Interesting - I didn't think that was the case for whole disk arrays -
>>> but there you go... Learnt something else :)
>> [snip]
>>>>> echo 4096> /sys/block/$i/queue/read_ahead_kb
>>>> Eliminate this line ^^^^
>>>
>>> Any insight into why? I would have thought that this would help -
>>> however I'm not quite sure as to the values - as this is much less than
>>> one chunk... That also being said, wouldn't it be a good idea to have
>>> *some* readahead?
>>
>> You read the answer up above, and commented on it. Maybe you didn't
>> fully understand? Or maybe it's because you don't know that these two
>> are functionally equivalent?
>>
>> blockdev --setra X
>> echo X> /sys/block/$i/queue/read_ahead_kb
>
> Ahhh - you're spot on... I didn't think they had the same functionality!
>
Btw, /sys/block/$i/queue/read_ahead_kb is deprecated, as its not a
kernel-internal queue setting, but rather bdi (backing device) related.
So /sys/block/$i/bdi/read_ahead_kb is recommended to be used (I guess
queue/read_ahead_kb will go away sometime in the future). In
/sys/class/bdi you can even control read-head of non-block device file
systems.
Cheers,
Bernd
prev parent reply other threads:[~2012-03-04 2:37 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-03-03 19:36 Speeding up chunk size change? Steven Haigh
2012-03-03 21:42 ` Stan Hoeppner
2012-03-04 0:56 ` Steven Haigh
2012-03-04 2:24 ` Stan Hoeppner
2012-03-04 2:27 ` Steven Haigh
2012-03-04 2:37 ` Bernd Schubert [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=4F52D565.7040604@fastmail.fm \
--to=bernd.schubert@fastmail.fm \
--cc=linux-raid@vger.kernel.org \
--cc=netwiz@crc.id.au \
--cc=stan@hardwarefreak.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).