[linux-audio-user] Low-Latency 2.4.x with ALSA

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Subject: [linux-audio-user] Low-Latency 2.4.x with ALSA
From: Joseph Zitt (jzitt_AT_metatronpress.com)
Date: Mon Jul 22 2002 - 01:50:15 EEST

I'm going through the steps in the Low-Latency 2.4.x with ALSA
mini-HOWTO.
It's quite good and clear, but a few issues have come up:

1) The document recommends doing the patch with the following:

cd /usr/src/
patch -p0 < /dir/where/you/put/2.4.x-low-latency.patch

However, as mentioned in earlier messages, it looks like doing

cd /usr/src/linux
patch -p1 < /dir/where/you/put/2.4.x-low-latency.patch

is more effective, since it avoids problems with a pathname that is
otherwise hardwired into the patch code.

2) The document points out places to change configuration options. In
doing a "make xconfig", some of these places are not visible, and it
would be worth noting the path down to them and undocumented additional
needed steps:

a) To enable "Control low latency with sysctl", I first had to enable
"Low latency scheduling" above it.

b) "IDE, ATA, and ATAPI block devices" is in a sub-window under
"ATA/IDE/MFM/RLL support" (surprisingly not, as I'd first guessed, under
the obvious "Block devices").

3) Looking at the description of the EXTRAVERSION information, I
couldn't quite figure out how the value in the example mapped to what it
was intended to describe.

4) And the one that has me stuck now: while the document has clear
instructions for setting up booting with LILO, I'm using GRUB. I'm not
seeing how to set up grub to use the new kernel, or whether the existing
setup will do the right thing. The /boot/grub/grub.conf file includes
references to files that have not changed or been updated, and I'm not
clear on whether it will work. Since I don't know whether continuing
without changing things there will result in an unbootable system, I'm
loth to experiment.

FWIW, my grub.conf has the following:

# grub.conf generated by anaconda
#
# Note that you do not have to rerun grub after making changes to this
# file NOTICE: You do not have a /boot partition. This means that
# all kernel and initrd paths are relative to /, eg.
# root (hd0,6)
# kernel /boot/vmlinuz-version ro root=/dev/hda7
# initrd /boot/initrd-version.img
#boot=/dev/hda
default=1
timeout=10
splashimage=(hd0,6)/boot/grub/splash.xpm.gz
title Red Hat Linux (2.4.18-3)
        root (hd0,6)
        kernel /boot/vmlinuz-2.4.18-3 ro root=/dev/hda7
        initrd /boot/initrd-2.4.18-3.img
title Red Hat Linux (New Kernel)
        root (hd0,6)
        kernel /boot/vmlinuz ro root=/dev/hda7
        initrd /boot/initrd-2.4.18-3.img
title Red Hat Linux (2.4.18-3)
        root (hd0,6)
        kernel /boot/vmlinuz-2.4.18-3 ro root=/dev/hda7
        initrd /boot/initrd-2.4.18-3.img
title Windows 98
        rootnoverify (hd0,0)
        chainloader +1

(Yeah, I never use the first and third ones, and am not sure why they're
there--but, again, worrying about breaking something into unbootability
if I mess with the grub.conf incorrectly.)

After doing the suggested

#

cp arch/i386/boot/bzImage /boot/bzImage-2.4.18
cp System.map /boot/System.map
  
I now have the following in /boot:

-rw-r--r-- 1 root root 5824 Jun 24 2001 boot.b
-rw-r--r-- 1 root root 1105371 Jul 21 15:07 bzImage-2.4.18
-rw-r--r-- 1 root root 612 Jun 24 2001 chain.b
-rw-r--r-- 1 root root 39947 Apr 18 04:45 config-2.4.18-3
drwxr-xr-x 2 root root 4096 Jun 4 11:16 grub
-rw-r--r-- 1 root root 126072 Jun 4 11:16
initrd-2.4.18-3.img
-rw-r--r-- 1 root root 473 May 30 23:01 kernel.h
-rw-r--r-- 1 root root 23108 Jun 24 2001 message
lrwxrwxrwx 1 root root 20 Jun 4 11:16 module-info ->
module-info-2.4.18-3
-rw-r--r-- 1 root root 14431 Apr 18 04:45
module-info-2.4.18-3
-rw-r--r-- 1 root root 640 Jun 24 2001 os2_d.b
lrwxrwxrwx 1 root root 19 Jun 4 11:16 System.map ->
System.map-2.4.18-3
-rw-r--r-- 1 root root 529786 Jul 21 15:39
System.map-2.4.18-3
-rwxr-xr-x 1 root root 3414559 Jun 4 09:43 vmlinux
-rwxr-xr-x 1 root root 2835238 Apr 18 04:45 vmlinux-2.4.18-3
lrwxrwxrwx 1 root root 16 Jun 4 11:16 vmlinuz ->
vmlinuz-2.4.18-3
-rw-r--r-- 1 root root 1030147 Apr 18 04:45 vmlinuz-2.4.18-3

All the "2.4.18-3" stuff is from what was in there before I started. I
find it particularly odd that copying the new System.map file into this
directory didn't change the file from being a link to an old value,
though cp gave no error.

I haven't gotten to the modutils section yet, but I'm seeing that I'll
have a few questions, such as a best source for the modutils package,
and good test arguments to see if modprobe or insprob were successful.

I also see that it says to do

cd /usr/src/linux
make modules; make modules_install

after booting into the new kernel, though it said to do so earlier, too,
in building the kernel. It's conceivable that it has to be done twice,
but I figure it's worth doublechecking.

... and eventually I'll actually get to the point where I install
ALSA... 

-- 
| josephzitt_AT_josephzitt.com                 http://www.josephzitt.com/ |
| http://www.metatronpress.com/jzitt/   http://www.mp3.com/josephzitt/ |
| == New book: Surprise Me with Beauty: the Music of Human Systems  == |
| Comma / Gray Code             Silence: the John Cage Discussion List |

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