The
operating system is said to be stable when both the software and
hardware of a machine or a system go parallel hand in hand. Your
favorite operating system or the best hardware that you opt for alone
cannot outperform to provide the best performance. Hence, if we
choose for the best hardware we have to tune the operating system
that we install to run efficiently on that hardware.
Optimizing
an operating system requires tuning of various parameters. These
parameters are a part of various software that an operating system
is built of. Hence tuning of all the parameters to their appropriate
values as required by the user to get the best performance gives the
best overall performance of the system.
One
of the most important factors to regulate the system's overall
performance is “Disk I/O Scheduler”. People normally wonder that
their system under performs even though they have latest processor, a
fast spinning hard disk and huge RAM, this is where the I/O
schedulers play their role particularly under heavy work loads. By
“heavy work loads” I mean to say that I can be running 3 virtual
machines, copying a Ubuntu iso file from host to guest, reading a
document, there's also an audio playing in the background, and web
browser in which I might be sending some mails. This might be too
much to handle for the operating system, I might face slow response
from the web browser or I might also get some trouble hearing the
song. This is where you will find the disk I/O scheduler being a
little laggy.
Disk
I/O is mainly categorized into sequential I/O and random I/O.
Sequential involves operating on one block immediately after it's neighbor In this type of I/O there is very little effect on the
response time as the disk drive head has to do the least work in
moving from one location to another. Whereas the random
I/O, on the other hand, involves large numbers of seeks and
rotations, which is usually much slower. We can know if our disk I/O
scheduler is sequential or random by determining the “average
request size” of each I/O operation. The “avgrq-sz” column from
iostat output shows the average request size per I/O operation. If
the average size per I/O operation is 16KB or less then it is random
disk I/O and if it is greater than 128KB then it is sequential disk
I/O. The below command shows average request size.
Every
operating system has a special software to communicate directly with
the computer's hardware called “kernel” and I/O scheduler is the
part of the kernel that handles read / write access to block storage
devices. It may be a a USB stick, local hard disk, or network file
system or any other storage environment that holds data in blocks. In
short I/O scheduler is the guy who decides how the bandwidth of the
disk has to be distributed to all of the applications simultaneously
or parallely that is ultimately based on the priority of the process.
A scheduler, queues and sequences the execution of read-write
requests, to manage mechanical latency and optimization of data
delivery performance. Latency is the seek time related to head travel
around the disk. Without an I/O scheduler, Linux kernel follows FIFO (First In, First Out) algorithm which can result in hard disk crashing. For example if one process is reading from one part of disk and writing to another part of the disk that will make the head move back and forth for every operation performed. A disk I/O scheduler's main goal to optimize the disk access time.
There
are four main I/O schedulers that we can find in Ubuntu namely noop,
cfq, deadline and anticipatory. Since anticipatory has become
obsolete, you wont find it in Ubuntu 12.04. Ubuntu 12.04 has got
“CFQ” as the default I/O scheduler whereas “deadline” is
default in Ubuntu 12.10.
Another
such I/O scheduler is BFQ (Budget Fair Queueing) which is based on
CFQ (Completely Fair Queueing). Queueing doesnt actually mean that
the requests will be arranged in FIFO (First-In-First-Out) order,
here queue means a container that contains or holds all the requests
that need to be manipulated further. BFQ was developed by Paolo
Valente, who is Assistant Professor of Computer Science at the
Department of Computer Science of University of Modena.
Installation
Using
Liquorix
Kernel - Why
drive when you can FLY?
The
three most important things for a good pc is cost, security and
performance. As we all know ubuntu linux is free and equally very
secure. What remains is performance. For performance there are many
guides available on internet. One particular way that I am always
interested in is to build a custom kernel. There are also
performance-focused kernels available. The Liquorix
kernel and Zen
kernel available at Damentz websites are built for performance
enhancement. Liquorix kernel is based on zen kernel. Another major
benefit of using this kernel is that it has integrated BFS
(Brain Fuck Scheduler, and yes that is what it is called) which is
the next best thing that money cant buy. BFS is a process scheduler
developed by Con
Kolivas.
We will discuss BFS in detail later.
Installing
Liquorix
kernel is very simple. To install Liquorix kernel in Ubuntu 12.04 /
12.10 one needs to install the latest gcc using "http://ppa.launchpad.net/ubuntu-toolchain-r/test/ubuntu precise main" ppa. Below shown is the
screenshot to add gcc repo in Update Manager.
$
sudo apt-get update
Now
install the latest gcc version. I found the latest gcc version to be
4.7 at the time of composing this post.
$
sudo apt-get install gcc-4.7 g++-4.7
$
sudo apt-get update
Install the Liquorix keyring.
$ sudo apt-get install '^liquorix-([^-]+-)?keyring.?'
$ sudo apt-get update
Search
for the latest liquorix kernel available using the below command.
$
sudo apt-cache search liquorix
Now
install Liquorix kernel.
$
sudo apt-get install liquorix*
After
installing, set the “GRUB_TIMEOUT” parameter value to “-1” in
/etc/default/grub file. After this you can see the list of kernels
after rebooting the machine, where you can select the liquorix kernel
to boot.
To list all the kernels installed in your system use the below mention command.
$ sudo dpkg --list | grep linux-image
There various benchmarking tools available for free like hdparm, iozone, bonnie++, phoronix test suite, stress, etc to test the performance of your system. Lastly
I would say everyone must once try “BFQ” and feel the difference,
though it is not yet seen in Ubuntu 12.10.
