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Subjectlibata, Sound on same IRQ : flaky sound

Hi,

I have a couple of AMD64 machines with onboard sound devices running
and they all have one thing in common : flaky sound when one is
doing some heavy disk I/O on the SATA disks. Interesting enough
/proc/interrupts shows that libata is using the same IRQ as the sound
devices :

model name : AMD Athlon(tm) 64 X2 Dual Core Processor 6000+
stepping : 3
cpu MHz : 3014.679
cache size : 1024 KB

# cat /proc/interrupts
CPU0 CPU1
0: 55869 154467838 IO-APIC-edge timer
8: 0 0 IO-APIC-edge rtc
9: 0 0 IO-APIC-level acpi
16: 1453 499686 IO-APIC-level libata, NVidia CK8S
17: 0 0 IO-APIC-level ehci_hcd:usb1
18: 27633 69978987 IO-APIC-level eth0
NMI: 10718 12112
LOC: 154533874 154533852
ERR: 0
MIS: 0

model name : AMD Opteron(tm) Processor 246
stepping : 10
cpu MHz : 1991.355
cache size : 1024 KB

# cat /proc/interrupts
CPU0 CPU1
0: 18108 19856365 IO-APIC-edge timer
1: 16 7915 IO-APIC-edge i8042
3: 0 56 IO-APIC-edge serial
4: 0 56 IO-APIC-edge serial
8: 0 0 IO-APIC-edge rtc
9: 0 0 IO-APIC-level acpi
12: 346 62269 IO-APIC-edge i8042
14: 0 190 IO-APIC-edge ide0
15: 1 189 IO-APIC-edge ide1
16: 827 358917 IO-APIC-level libata, AMD AMD8111
17: 0 18 IO-APIC-level ohci_hcd:usb1, ohci_hcd:usb2
18: 555 231470 IO-APIC-level HiSax, nvidia
19: 15179 3489796 IO-APIC-level eth0
NMI: 211 511
LOC: 19871720 19871628
ERR: 0
MIS: 0

Kernel is 2.6.15,

Preemption Model is (Preemptible Kernel (Low-Latency Desktop)), Memory
model is (Flat Memory), [*] Preempt The Big Kernel Lock is switched on.
Timer frequency is (1000 HZ) or (100 HZ), but changing this value is
of no influence. One of the machines is a genuine dual Opteron machine
but i'm rather disappointed with the NUMA capabilities of
the 2.6.15 kernel. It does do NUMA, but thats all it does, it doesn't
add anything compared to a SMP kernel with NUMA switched off.

Does one really need the PREEMPT_RT approach to get rock solid
sound as described here ? :

"A realtime preemption overview"
by Paul McKenney, August 10, 2005
http://lwn.net/Articles/146861/

How about giving your sound device a proper seperate IRQ number?
At least libata should like eth0 have its own kernel resources.

Regards,

Robert
PS. please also cc: to my email address.
--
Robert M. Stockmann - RHCE
Network Engineer - UNIX/Linux Specialist
crashrecovery.org stock@stokkie.net



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