Re: OT : BSD vs Linux was Re : Boot loaders for Linux that can also boot FreeBSD

[Ralf Mardorf <ralf.mardorf@rocketmail.com>]

On Sat, 2012-12-01 at 01:07 +0100, berenger.morel@neutralite.org wrote:
> I have questions about why are you needing so much kernels.

My apologies, I'm short in time, so my off-list mail also is short and
slightly OT.

On the quick:

I need that much kernels, because I've got issues with audio latency and
had issues with MIDI jitter.

I try to keep the most stable Linux for my needs and try to get a Linux,
that will fit better to my needs.

I've got no experiences with FreeBSD, I don't know the difference
myself.

IOW I try to fix issues, without buying hardware. On old computers it
was easy to get hard real-time, because the software directly was
connected with the hardware and the kernels where optimized to the
hardware. Computers today have many layers, different chipsets, do real
multitasking, but this does cause timing issues.

For example, using older kernels my graphics and the audio card do share
the same IRQ, with the new kernel the graphics get another IRQ:

spinymouse@q:~$ uname -a
Linux q 3.6.5-rt14 #1 SMP PREEMPT RT Fri Nov 2 21:36:37 CET 2012 x86_64
x86_64 x86_64 GNU/Linux
spinymouse@q:~$ service rtirq status

  PID CLS RTPRIO  NI PRI %CPU STAT COMMAND	
   62 FF      90   - 130  0.0 S    irq/8-rtc0	
  799 FF      85   - 125  0.0 S    irq/18-snd_hdsp	
  830 FF      85   - 125  0.0 S    irq/20-snd_ice1	
  832 FF      85   - 125  0.0 S    irq/21-snd_ice1	
   54 FF      80   - 120  0.0 S    irq/19-ehci_hcd	
   55 FF      80   - 120  0.0 S    irq/16-ohci_hcd	
   56 FF      79   - 119  0.0 S    irq/17-ohci_hcd	
   58 FF      78   - 118  0.0 S    irq/18-ohci_hcd	
   59 FF      78   - 118  0.0 S    irq/17-ohci_hcd	
   60 FF      77   - 117  0.0 S    irq/18-ohci_hcd	
   61 FF      75   - 115  0.0 S    irq/1-i8042	
   24 FF      50   -  90  0.0 S    irq/9-acpi	
   46 FF      50   -  90  0.0 S    irq/22-ahci	
  216 FF      50   -  90  0.0 S    irq/14-pata_ati	
  218 FF      50   -  90  0.0 S    irq/15-pata_ati	
  302 FF      50   -  90  0.0 S    irq/22-firewire	
  580 FF      50   -  90  0.0 S    irq/7-parport0	
  782 FF      50   -  90  0.0 S    irq/43-radeon	
 1313 FF      50   -  90  0.0 S    irq/42-eth0	
    3 FF       1   -  41  0.1 S    ksoftirqd/0	
   15 FF       1   -  41  0.1 S    ksoftirqd/1

If I would make music, I would unbind other things that share IRQ 18 too
by running a script:

spinymouse@q:/mnt/music/quantal/01song$ cat tuning
#!/bin/bash

# sudo bash tuning - Ubuntu Studio Quantal
# 2012/Nov/04

### http://www.mythtv.org/wiki/PCI_Latency
###
http://wiki.linuxmusicians.com/doku.php?id=system_configuration#pci_bus_latency

### Bluetooth
service bluetooth stop

### Network
#service network-manager stop
#service networking stop # does cause serious issues
#modprobe -r r8169 # Ethernet NIC driver

### TerraTec EWX 24/96
modprobe -r snd_ice1712

### Others
modprobe -r firewire-ohci
modprobe -r firewire_core
service cups stop
modprobe -r ppdev # parallel port
modprobe -r lp    # printer

### Unbinding devices
echo -n "0000:00:13.2" > /sys/bus/pci/drivers/ohci_hcd/unbind
echo -n "0000:00:13.4" > /sys/bus/pci/drivers/ohci_hcd/unbind

### Log file
l="log/tuning.log"
#echo "$ lspci -v                       "  > $l
#lspci -v                                 >> $l
#echo                                     >> $l
echo "$ /etc/init.d/rtirq status       "  > $l
/etc/init.d/rtirq status                 >> $l
echo "$ grep 18: /proc/interrupts"       >> $l
grep 18: /proc/interrupts                >> $l
echo                                     >> $l
echo -n $(date)" - "$(uname -r)" - "     >> $l
cat /etc/issue                           >> $l
echo "##############################" ; cat $l

exit 0

This is neither needed for professional servers nor needed for averaged
desktop usage. Real-time audio is a special task. For real-time CNC
there is another real-time kernel. This are things most users don't need
to care about.

Regards,
Ralf