Mailing List Archive: Linux: Kernel

Kernel Options: To use MSI-X or not?

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jpiszcz at lucidpixels

Nov 4, 2009, 8:53 AM

Post #1 of 4 (61 views)
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Kernel Options: To use MSI-X or not?

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.
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Valdis.Kletnieks at vt

Nov 4, 2009, 9:36 AM

Post #2 of 4 (58 views)
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Re: Kernel Options: To use MSI-X or not? [In reply to]

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

hancockrwd at gmail

Nov 4, 2009, 4:04 PM

Post #3 of 4 (53 views)
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Re: Kernel Options: To use MSI-X or not? [In reply to]

On 11/04/2009 11:36 AM, Valdis.Kletnieks[at]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.
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hancockrwd at gmail

Nov 4, 2009, 4:05 PM

Post #4 of 4 (53 views)
Permalink

Re: Kernel Options: To use MSI-X or not? [In reply to]

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.
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the body of a message to majordomo[at]vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

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