readahead default configuration hurts the system performance

[Jérôme]

Hello,

I think the default "readahead" configuration hurts the system performance.

Just an example:
---
m@m-desktop:~$ grep modules /etc/readahead/boot | head -5
/lib/linux-restricted-modules/2.6.24-16-generic/ath_hal/ah_os.o
/lib/linux-restricted-modules/2.6.24-16-generic/ath_hal/ath_hal.mod.o
/lib/linux-restricted-modules/2.6.24-16-generic/ath_hal/i386-elf.hal.o
/lib/linux-restricted-modules/2.6.24-16-generic/fcdsl/dbgif.o
/lib/linux-restricted-modules/2.6.24-16-generic/fcdsl/driver.o
m@m-desktop:~$ grep -v "^#" /boot/grub/menu.lst |grep -i "^kernel"
kernel /vmlinuz-2.6.24-23-generic root=UUID=b3ea2423-5081-46dc-a6e3-e46987f99f3e ro quiet splash
kernel /vmlinuz-2.6.24-23-generic root=UUID=b3ea2423-5081-46dc-a6e3-e46987f99f3e ro single
kernel /vmlinuz-2.6.24-22-generic root=UUID=b3ea2423-5081-46dc-a6e3-e46987f99f3e ro quiet splash
kernel /vmlinuz-2.6.24-22-generic root=UUID=b3ea2423-5081-46dc-a6e3-e46987f99f3e ro single
kernel /vmlinuz-2.6.24-19-generic root=UUID=b3ea2423-5081-46dc-a6e3-e46987f99f3e ro quiet splash
kernel /vmlinuz-2.6.24-19-generic root=UUID=b3ea2423-5081-46dc-a6e3-e46987f99f3e ro single
kernel /memtest86+.bin
m@m-desktop:~$
---

I think:
- either "readahead" should avoid caching the version dependent files (like "2.6.24-16" kernel modules)
- or you should remove "readahead" from "ubuntu-desktop" package dependencies (and possibly replace it with "preload")

Regards.

[Scott James Remnant (Canonical) (canonical-scott)]

I prune the kernel modules out of the readahead lists before I generate them, sometimes I admittedly get it wrong, but this is generally human error not a bug

[Jérôme (jerome-bouat)]

Hello Scott,

Thanks for the explanation.

Why is ubuntu not using "preload" ?

FYI,
I replaced "readahead" by "preload" on the below system
and it made it faster:
- CPU: AMD Athlon XP 1500+
- mem: 392 MB
- Ubuntu version: hardy
- minimum total size of the used files of the tracked processes: 4MB

> Message du 27/01/09 13:45
> De : "Scott James Remnant"
> A : <email address hidden>
> Copie à :
> Objet : [Bug 318505] Re: readahead default configuration hurts the systemperformance
>
>
> I prune the kernel modules out of the readahead lists before I generate
> them, sometimes I admittedly get it wrong, but this is generally human
> error not a bug
>
> ** Changed in: readahead (Ubuntu)
> Status: New => Invalid
>
> --
> readahead default configuration hurts the system performance
> https://bugs.launchpad.net/bugs/318505
> You received this bug notification because you are a direct subscriber
> of the bug.
>
>

[Scott James Remnant (Canonical) (canonical-scott)]

On Tue, 2009-01-27 at 16:15 +0000, Jérôme wrote:

> Why is ubuntu not using "preload" ?
>
preload, readahead, prefetch, sreadahead, etc. are all just variations
on a theme.

We currently use readahead, and don't have compelling reasons to switch
to the others - since they introduce just as many problems as they
solve.

Scott
--
Scott James Remnant
<email address hidden>