Kernel Options: To use MSI-X or not?

Kernel Options: To use MSI-X or not?

[Justin Piszcz]

Hello,

I was curious whether its best to use MSI-X when the driver supports it or 
not?

Example, 3ware cards/Intel Audio Drivers you can use MSI-X instead of 
having several devices use/share an interrupt.

What are the pros/cons to using MSI-X vs. having devices share an IRQ?

Justin.

Re: Kernel Options: To use MSI-X or not?

[Valdis.Kletnieks]

[-- Attachment #1: Type: text/plain, Size: 2731 bytes --]

On Wed, 04 Nov 2009 11:53:18 EST, Justin Piszcz said:

> Example, 3ware cards/Intel Audio Drivers you can use MSI-X instead of 
> having several devices use/share an interrupt.
> 
> What are the pros/cons to using MSI-X vs. having devices share an IRQ?

Cons: Sometimes, you'll find a device that claims to support MSI but in fact is
to some extent borked...

I'm the proud owner of a Dell Latitude D820, which includes this PCI:

00:1b.0 Audio device: Intel Corporation 82801G (ICH7 Family) High Definition Audio Controller (rev 01)
        Subsystem: Dell Device 01cc
        Flags: bus master, fast devsel, latency 0, IRQ 30
        Memory at efffc000 (64-bit, non-prefetchable) [size=16K]
        Capabilities: [50] Power Management version 2
        Capabilities: [60] MSI: Enable+ Count=1/1 Maskable- 64bit+
        Capabilities: [70] Express Root Complex Integrated Endpoint, MSI 00
        Capabilities: [100] Virtual Channel <?>
        Capabilities: [130] Root Complex Link <?>
        Kernel driver in use: HDA Intel

However, actually trying to enable MSI gets me this at some pseudo-random
time after booting (one for each of 7 boots):

[    4.519264] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00df0900
[   22.788015] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x008f0c00
[    4.719263] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00df0900
[   12.497263] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00df0900
[  815.350265] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00df0900
[  595.171267] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00171700
[    4.968263] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00df0900

(Am slightly mystified about the resets at 4 and 12 seconds - at that point,
we're not up far enough to actually try to use the audio. I suspect udev trying
to initialize the card - except sometimes it works and runs just fine with
MSI for quite some time:

[14267.701267] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00df0900
[12841.892050] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00df0900
[10647.783274] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x001f1500
[15091.102034] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00171700
[20085.955293] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00df0700



[-- Attachment #2: Type: application/pgp-signature, Size: 227 bytes --]

Re: Kernel Options: To use MSI-X or not?

[Robert Hancock]

On 11/04/2009 11:36 AM, Valdis.Kletnieks@vt.edu wrote:
> On Wed, 04 Nov 2009 11:53:18 EST, Justin Piszcz said:
>
>> Example, 3ware cards/Intel Audio Drivers you can use MSI-X instead of
>> having several devices use/share an interrupt.
>>
>> What are the pros/cons to using MSI-X vs. having devices share an IRQ?
>
> Cons: Sometimes, you'll find a device that claims to support MSI but in fact is
> to some extent borked...
>
> I'm the proud owner of a Dell Latitude D820, which includes this PCI:
>
> 00:1b.0 Audio device: Intel Corporation 82801G (ICH7 Family) High Definition Audio Controller (rev 01)
>          Subsystem: Dell Device 01cc
>          Flags: bus master, fast devsel, latency 0, IRQ 30
>          Memory at efffc000 (64-bit, non-prefetchable) [size=16K]
>          Capabilities: [50] Power Management version 2
>          Capabilities: [60] MSI: Enable+ Count=1/1 Maskable- 64bit+
>          Capabilities: [70] Express Root Complex Integrated Endpoint, MSI 00
>          Capabilities: [100] Virtual Channel<?>
>          Capabilities: [130] Root Complex Link<?>
>          Kernel driver in use: HDA Intel
>
> However, actually trying to enable MSI gets me this at some pseudo-random
> time after booting (one for each of 7 boots):
>
> [    4.519264] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00df0900
> [   22.788015] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x008f0c00
> [    4.719263] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00df0900
> [   12.497263] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00df0900
> [  815.350265] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00df0900
> [  595.171267] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00171700
> [    4.968263] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00df0900
>
> (Am slightly mystified about the resets at 4 and 12 seconds - at that point,
> we're not up far enough to actually try to use the audio. I suspect udev trying
> to initialize the card - except sometimes it works and runs just fine with
> MSI for quite some time:
>
> [14267.701267] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00df0900
> [12841.892050] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00df0900
> [10647.783274] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x001f1500
> [15091.102034] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00171700
> [20085.955293] ALSA sound/pci/hda/hda_intel.c:683: No response from codec, disabling MSI: last cmd=0x00df0700

This may not be an actual MSI problem (in fact I'd say it's probably 
not). Currently hda_intel disables MSI after any codec response timeout, 
so it could be it would have worked if it retried while still using MSI. 
I believe Takashi was going to change the driver to be less sensitive 
about this.

Re: Kernel Options: To use MSI-X or not?

[Robert Hancock]

On 11/04/2009 10:53 AM, Justin Piszcz wrote:
> Hello,
>
> I was curious whether its best to use MSI-X when the driver supports it
> or not?
>
> Example, 3ware cards/Intel Audio Drivers you can use MSI-X instead of
> having several devices use/share an interrupt.
>
> What are the pros/cons to using MSI-X vs. having devices share an IRQ?

Normally using MSI/MSI-X is always better (or at least no worse), 
assuming it works properly on the system and on the device.. Hopefully 
by this point we've fixed most or all the system-related problems or 
forced MSI off on platforms where it can't work properly.