APIC priorities, can they be changed?

APIC priorities, can they be changed?

[Mike Panetta]

I am not on the list (corperate email sucks) so please CC any replies to 
me.  Thanks.

I am working on a project that has run in to what seems to be an 
interrupt priority problem.  We switched mainboards in our product and 
went from a system where the EHCI controller IRQ was of a fairly high 
priority to one where its the lowest in the system.  Now we cannot get 
the data off our USB device in time and we drop alot of data.  I was 
hoping someone here may have a simple(ish) solution to the problem.

I have seen the preempt patches, but they touch a lot of files, and we 
have gone through testing with the 2.6.16.19 kernel and do not wish to 
change, and we cannot find a version of the patch for this kernel. Is 
there something smaller/simpler I can do?  My understanding is the 
priority in the APIC is set in software via the interrupt vector number 
(higher numbers have lower priority) is this true?  If so, how hard 
would it be for me to just change the vector numbers around?

Ideally I would love to switch to the 2.6.20 kernel and use the preempt 
patch, but I doubt we have the time for that.

Thanks,
Mike

Re: APIC priorities, can they be changed?

[linux-os (Dick Johnson)]

On Thu, 15 Feb 2007, Mike Panetta wrote:

> I am not on the list (corperate email sucks) so please CC any replies to
> me.  Thanks.
>
> I am working on a project that has run in to what seems to be an
> interrupt priority problem.  We switched mainboards in our product and
> went from a system where the EHCI controller IRQ was of a fairly high
> priority to one where its the lowest in the system.  Now we cannot get
> the data off our USB device in time and we drop alot of data.  I was
> hoping someone here may have a simple(ish) solution to the problem.
>
> I have seen the preempt patches, but they touch a lot of files, and we
> have gone through testing with the 2.6.16.19 kernel and do not wish to
> change, and we cannot find a version of the patch for this kernel. Is
> there something smaller/simpler I can do?  My understanding is the
> priority in the APIC is set in software via the interrupt vector number
> (higher numbers have lower priority) is this true?  If so, how hard
> would it be for me to just change the vector numbers around?
>
> Ideally I would love to switch to the 2.6.20 kernel and use the preempt
> patch, but I doubt we have the time for that.
>
> Thanks,
> Mike

Can't you muck with the BIOS settings? That's where the primary
hardware gets 'connected'.


Cheers,
Dick Johnson
Penguin : Linux version 2.6.16.24 on an i686 machine (5592.61 BogoMips).
New book: http://www.AbominableFirebug.com/
_
\x1a\x04

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The information transmitted in this message is confidential and may be privileged.  Any review, retransmission, dissemination, or other use of this information by persons or entities other than the intended recipient is prohibited.  If you are not the intended recipient, please notify Analogic Corporation immediately - by replying to this message or by sending an email to DeliveryErrors@analogic.com - and destroy all copies of this information, including any attachments, without reading or disclosing them.

Thank you.

Re: APIC priorities, can they be changed?

[Mike Panetta]

linux-os (Dick Johnson) wrote:
>
> On Thu, 15 Feb 2007, Mike Panetta wrote:
>
> > I am not on the list (corperate email sucks) so please CC any replies to
> > me.  Thanks.
[snip]
> > I have seen the preempt patches, but they touch a lot of files, and we
> > have gone through testing with the 2.6.16.19 kernel and do not wish to
> > change, and we cannot find a version of the patch for this kernel. Is
> > there something smaller/simpler I can do?  My understanding is the
> > priority in the APIC is set in software via the interrupt vector number
> > (higher numbers have lower priority) is this true?  If so, how hard
> > would it be for me to just change the vector numbers around?
> >
[snip]
> > Thanks,
> > Mike
>
> Can't you muck with the BIOS settings? That's where the primary
> hardware gets 'connected'.
>

I did try that.  The BIOS only allows me to either allocate an IRQ to be 
a PCI interrupt, or reserve it (for what I have no idea).  The IRQ's 
listed in the BIOS are also different from the ones Linux sees.  I think 
the BIOS is seeing the XT-PIC IRQ numbers and Linux is seeing the APIC 
numbers.  For example the little bios blurb that prints before the 
system boots says the USB controller I am interested in is 
assigned/using IRQ 10, Linux sees it using IRQ 18.

I have found that I can keep Linux from using the APIC by disabling it 
with a kernel command line switch, but that does not help, it just makes 
Linux use the XT-PIC instead of the IO-APIC to do IRQ routing.

So I guess I'm back to my original question of  'Would changing the 
vector numbers do what I want?' and if the answer is 'yes', how would I 
do it?

Thanks,
Mike

>
> Cheers,
> Dick Johnson
> Penguin : Linux version 2.6.16.24 on an i686 machine (5592.61 BogoMips).
> New book: http://www.AbominableFirebug.com/
> _
> \x1a\x04
>
> ****************************************************************
> The information transmitted in this message is confidential and may be 
> privileged.  Any review, retransmission, dissemination, or other use 
> of this information by persons or entities other than the intended 
> recipient is prohibited.  If you are not the intended recipient, 
> please notify Analogic Corporation immediately - by replying to this 
> message or by sending an email to DeliveryErrors@analogic.com 
> <mailto:DeliveryErrors@analogic.com> - and destroy all copies of this 
> information, including any attachments, without reading or disclosing 
> them.
>
> Thank you.
>

Re: APIC priorities, can they be changed?

[Florian Schmidt]

On Thursday 15 February 2007, Mike Panetta wrote:
> I did try that.  The BIOS only allows me to either allocate an IRQ to be
> a PCI interrupt, or reserve it (for what I have no idea).  The IRQ's
> listed in the BIOS are also different from the ones Linux sees.  I think
> the BIOS is seeing the XT-PIC IRQ numbers and Linux is seeing the APIC
> numbers.  For example the little bios blurb that prints before the
> system boots says the USB controller I am interested in is
> assigned/using IRQ 10, Linux sees it using IRQ 18.
>
> I have found that I can keep Linux from using the APIC by disabling it
> with a kernel command line switch, but that does not help, it just makes
> Linux use the XT-PIC instead of the IO-APIC to do IRQ routing.
>
> So I guess I'm back to my original question of  'Would changing the
> vector numbers do what I want?' and if the answer is 'yes', how would I
> do it?

With XT-PIC, there was a way to change the priotrities used by the IRQ. It was 
called irqtune iirc.

Ah ya,

http://cae.best.vwh.net/irqtune/

Dunno if there's something similar available for APIC..

Regards,
Flo

-- 
Palimm Palimm!
http://tapas.affenbande.org