linux-kernel - Re: [PATCH] pci: change msi-x vector to 32bit

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Date:	Sat, 16 Aug 2008 16:21:41 -0700
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"James Bottomley" <James.Bottomley@...senpartnership.com>
Cc:	"Alan Cox" <alan@...rguk.ukuu.org.uk>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Jesse Barnes" <jbarnes@...tuousgeek.org>,
	"Ingo Molnar" <mingo@...e.hu>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	"Andrew Vasquez" <andrew.vasquez@...gic.com>
Subject: Re: [PATCH] pci: change msi-x vector to 32bit

On Sat, Aug 16, 2008 at 4:09 PM, James Bottomley
<James.Bottomley@...senpartnership.com> wrote:
> On Sat, 2008-08-16 at 15:17 -0700, Yinghai Lu wrote:
>> On Sat, Aug 16, 2008 at 1:45 PM, James Bottomley
>> <James.Bottomley@...senpartnership.com> wrote:
>> >> > What I still don't quite get is the benefit of large IRQ spaces ...
>> >> > particularly if you encode things the system doesn't really need to know
>> >> > in them.
>> >>
>> >> then set nr_irqs = nr_cpu_ids * NR_VECTORS))
>> >> and count down for msi/msi-x?
>> >
>> > No, what I mean is that msis can trip directly to CPUs, so this is an
>> > affinity thing (that MSI is directly bound to that CPU now), so in the
>> > matrixed way we display this in show_interrupts() with the CPU along the
>> > top and the IRQ down the side, it doesn't make sense to me to encode IRQ
>> > affinity in the irq number again.   So it makes more sense to assign the
>> > vectors based on both the irq number and the CPU affinity so that if the
>> > PCI MSI for qla is assigned to CPU4 you can reassign it to CPU5 and so
>> > on.
>>
>> msi-x entry index, cpu_vector, irq number...
>>
>> you want to different cpus have same vector?
>
> Obviously I'm not communicating very well.  Your apparent assumption is
> that irq number == vector.  What I'm saying is that's not what we've
> done for individually vectored CPU interrupts in other architectures.
> In those we did (cpu no, irq) == vector.  i.e. the affinity and the irq
> number identify the vector.  For non-numa systems, this is effectively
> what you're interested in doing anyway.  For numa systems, it just
> becomes a sparse matrix.
>
msix_entry.vector == irq.

and cpu have per_cpu(vector_irq), and use that cpu get irq number.

when irq migratition, different cpu could use different vector for same irq.
or say phys_flat mode, same vector in different cpus could server different irq.
it seems x86 (64 bit) and ia64 already did that.

YH
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