Re: [LAU] midi keyboards, jackd, low latency

tizo wrote:
> Hi there,
>
> Sorry about my previous mail. I was just starting to write a draft
> about the topics I want to ask, and I accidentally push the send
> button.
>
> Well, my goal is to play two midi keyboards, sending the events
> through jackd, to qsynth. My computer is a Laptop HP 550, with HDA
> Intel sound card, 3 GB of memory, and a Core 2 DUO CPU of 1.40 GHz. My
> OS is UbuntuStudio 8.04, with kernel 2.6.24-23-rt.
>
> First of all, I cannot run jackd without xruns, if I configure it with
> 32 frames per period, or less. I am running it as root, with realtime,
> and a priority of 70. As soon as I run it, it starts to count xruns,
> and I am only executing jackd.
>
> Looking at the different IRQ, I have saw that my sound card is sharing
> the IRQ 16 with an USB port, and the video driver. This is a cat of
> /proc/interrupts:
>
> CPU0 CPU1
> 0: 1026591 1099066 IO-APIC-edge timer
> 1: 2060 839 IO-APIC-edge i8042
> 8: 0 1 IO-APIC-edge rtc
> 9: 121 95 IO-APIC-fasteoi acpi
> 12: 118454 56308 IO-APIC-edge i8042
> 14: 6410 5638 IO-APIC-edge libata
> 15: 5167 6228 IO-APIC-edge libata
> 16: 624 482 IO-APIC-fasteoi uhci_hcd:usb1, HDA
> Intel, i915@email-addr-hidden:0000:00:02.0
> 17: 24009 14458 IO-APIC-fasteoi eth1
> 18: 0 0 IO-APIC-fasteoi ehci_hcd:usb2, uhci_hcd:usb5
> 20: 0 0 IO-APIC-fasteoi uhci_hcd:usb3, ehci_hcd:usb6
> 21: 0 0 IO-APIC-fasteoi uhci_hcd:usb4
> 508: 378 139 PCI-MSI-edge eth0
> NMI: 0 0 Non-maskable interrupts
> LOC: 295845 239602 Local timer interrupts
> RES: 34174 96493 Rescheduling interrupts
> CAL: 10832 457 function call interrupts
> TLB: 873 742 TLB shootdowns
> TRM: 0 0 Thermal event interrupts
> THR: 0 0 Threshold APIC interrupts
> SPU: 0 0 Spurious interrupts
> ERR: 0
>
> I have searched a lot on Internet, and even in the list, and I have
> not found a way to change the IRQ assignments. In fact, I have read
> some mails that said that I can't do that in a laptop (except in some
> Thinkpads, where IRQ can be changed in the BIOS), as in PCs this can
> be done changing the card to other slot. In other places, some kernel
> parameters were suggested to obtain other IRQ assignments, but the
> only parameter that change those in my computer, was "acpi=off", and
> it was not better. In this case, /proc/interrupts shows the following:
>
> CPU0
> 0: 602 XT-PIC-XT timer
> 1: 209 XT-PIC-XT i8042
> 2: 0 XT-PIC-XT cascade
> 8: 0 XT-PIC-XT rtc
> 10: 2912 XT-PIC-XT uhci_hcd:usb1, uhci_hcd:usb3,
> uhci_hcd:usb4, ehci_hcd:usb6, eth1, HDA Intel, i915@email-addr-hidden:0000:00:02.0
> 11: 0 XT-PIC-XT ehci_hcd:usb2, uhci_hcd:usb5
> 12: 5196 XT-PIC-XT i8042
> 14: 9987 XT-PIC-XT libata
> 15: 704 XT-PIC-XT libata
> 508: 31 PCI-MSI-edge eth0
> NMI: 0 Non-maskable interrupts
> LOC: 87955 Local timer interrupts
> RES: 0 Rescheduling interrupts
> CAL: 0 function call interrupts
> TLB: 0 TLB shootdowns
> TRM: 0 Thermal event interrupts
> THR: 0 Threshold APIC interrupts
> SPU: 0 Spurious interrupts
> ERR: 0
>
> So, my first question is: is there a way to change my IRQ assignment?,
> or that really cannot be done in my laptop? I would like to have it in
> a not shared one, not necessarily in IRQ 9, as with rt kernel a
> priority raise of an IRQ can be done with chrt.
>

Probably not. But check your bios anyway just in case you can reassign
the irq there.

> I have also read, that the HDA sound card is not good for audio
> processing. I am just starting to configure my whole "synthetizer
> box", so by this time, I am only making some tests with it. But, for
> the near future, which usb sound card would you recommend?.
>
>

The hda should give you reasonable audio quality and performance but you
will get better of both worlds with a professional sound card.

Make sure it is usb-2.0 capable if you must use a usb sound card. You
could also look into a firewire device which tend to have better latency
performance.

> I also wonder that, if the IRQ of USB ports cannot be change too, I
> would have some of them sharing some IRQ. Would that affect the
> performance, having an usb sound card?. And what about the performance
> of the midi events for the keyboards connected to the laptop?.
>
>

If you can get the realtime kernel running it will improve latency
performance. But you might find that a standard kernel is good enough
for your general needs.

> Thanks very much,
>
> tizo
> _______________________________________________
> Linux-audio-user mailing list
> Linux-audio-user@email-addr-hidden
> http://lists.linuxaudio.org/mailman/listinfo/linux-audio-user
>

-- 
Patrick Shirkey
Boost Hardware Ltd.
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