linux-kernel - Re: [PATCH 1/3] i/o bandwidth controller documentation

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Date:	Sat, 21 Jun 2008 12:35:02 +0200
From:	Andrea Righi <righi.andrea@...il.com>
To:	Randy Dunlap <randy.dunlap@...cle.com>
CC:	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Paul Menage <menage@...gle.com>,
	Carl Henrik Lunde <chlunde@...g.uio.no>, axboe@...nel.dk,
	matt@...ehost.com, roberto@...it.it,
	Divyesh Shah <dpshah@...gle.com>, akpm@...ux-foundation.org,
	containers@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] i/o bandwidth controller documentation

Thanks Randy, I've applied all your fixes to my local documentation,
next patchset version will include them. A few small comments below.

Randy Dunlap wrote:
>> +* Run a benchmark doing I/O on /dev/sda1 and /dev/sda5; I/O limits and usage
>> +  defined for cgroup "foo" can be shown as following:
>> +  # cat /mnt/cgroup/foo/blockio.bandwidth
>> +  === device (8,1) ===
>> +    bandwidth limit: 1024 KiB/sec
>> +  current i/o usage: 819 KiB/sec
>> +  === device (8,5) ===
>> +    bandwidth limit: 1024 KiB/sec
>> +  current i/o usage: 3102 KiB/sec
> 
> Ugh, this makes it look like the output does "pretty printing" (formatting),
> which is generally not a good idea.  Let some app be responsible for that,
> not the kernel.  Basically this means don't use leading spaces just to make the
> ":"s line up in the output.

Sounds reasonable. I think the output could be further reduced,
the following format should be explanatory enough.

device: %u,%u
bandwidth: %lu KiB/sec
usage: %lu KiB/sec

>> +WARNING: per-block device limiting rules always refer to the dev_t device
>> +number. If a block device is unplugged (i.e. a USB device) the limiting rules
>> +associated to that device persist and they are still valid if a new device is
> 
> associated with (?)

what about:

...the limiting rules defined for that device...

-Andrea
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