linux-kernel - Re: Multiple MSI

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Date:	Mon, 7 Jul 2008 10:51:07 -0600
From:	Grant Grundler <grundler@...isc-linux.org>
To:	Matthew Wilcox <matthew@....cx>
Cc:	Grant Grundler <grundler@...isc-linux.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	linux-pci@...r.kernel.org,
	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	David Miller <davem@...emloft.net>,
	Dan Williams <dan.j.williams@...el.com>,
	Martine.Silbermann@...com, linux-kernel@...r.kernel.org,
	Michael Ellerman <michaele@....ibm.com>
Subject: Re: Multiple MSI

On Mon, Jul 07, 2008 at 10:39:19AM -0600, Matthew Wilcox wrote:
...
> > If the Local-APICs are able to redirect interrupts, then multiple CPUs
> > can process the interrupts.
> 
> That's not the only way it can work.  If you have an APIC per root bus,
> you can target that with the write.  The APIC could then map the
> interrupt request to the appropriate CPU.  In this scenario, programming
> affinity would be twiddling some bits in the APIC and not need to write
> to the device's MSI register at all.

Ok...but that still means it's got only one target (either one CPU
or a group of CPUs).

> What I've implemented for x86-64 can target any mask of CPUs that are
> in the same interrupt domain.  My machine only has one interrupt domain,
> so I can target the MSI to any subset of the CPUs.  They all move
> together, so you can't target a different subset of CPUs for different
> MSIs on the same device.

*nod* - that's what I meant.

thanks,
grant
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