Disk I/O as a bottleneck?

[Gilboa Davara]

On Mon, 2011-05-09 at 06:29 +0300, Omer Zak wrote:
> [This E-mail message is bottom-posting contrary to my usual custom.]

Thanks :)


> > 1. Kernel version?
> > 2.6.38 added a very small patch that that done wonders to eliminate
> > foreground process scheduling issues that plagued desktop setups since
> > the introduction of the CFS scheduler*. (Google for +2.6.38 +group
> > +scheduling)
> > On my Fedora 14 + 2.6.38 / dual 6C Xeon workstation I can easily
> > watching a DVD movies while compiling the kernel and running a couple of
> > VM's (using qemu-kvm) in the background. Doing the same using the stock
> > Fedora 14 2.6.35 kernel is... err... interesting experience :)
> 
> Standard Debian Squeeze kernel:
> $ uname -a
> Linux c4 2.6.32-5-vserver-amd64 #1 SMP Mon Mar 7 23:14:47 UTC 2011
> x86_64 GNU/Linux

I'd consider trying a kernel from debian-testing or rolling your own.
As I said, at least in my experience, the interface "feel" of 2.6.38 is
-far-, -far- better than previous kernels.

> > 2. Are you sure your SATA is in AHCI mode?
> > (Simply type: $ find /sys/devices | grep ahci)
> 
> My SATA indeed runs in non-AHCI mode.
> 
> The question now is how to configure it to run in AHCI mode?
> According to the Wikipedia article
> http://en.wikipedia.org/wiki/Advanced_Host_Controller_Interface, I need
> to modify a BIOS setting and maybe create a new initrd image.
> Another source:
> http://www.techmetica.com/howto/sata-ahci-mode-bios-setting.-what-does-it-do/
> 
> I can handle the BIOS setting but how to check whether a new initrd
> image is needed, and if necessary create it?

First you'll need to enable it in your BIOS. (Usually under SATA
controller mode, under advanced settings)
If you cannot seem to find this option, trying searching for a BIOS
upgrade for your motherboard.
If it's enabled, and somehow your kernel haven't picked it up, check
that CONFIG_SATA_AHCI is enabled in your kernel .confing. ($
cat /boot/*config* | grep AHCI)
... If it does, you may need an updated kernel that better supports your
SATA chipset. (Which board is it?)

- Gilboa