linux-kernel - Re: Multiple MSI, take 4

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Date:	Sat, 12 Jul 2008 17:37:20 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Matthew Wilcox <matthew@....cx>
Cc:	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	grundler@...isc-linux.org, mingo@...e.hu, tglx@...utronix.de,
	jgarzik@...ox.com, linux-ide@...r.kernel.org,
	suresh.b.siddha@...el.com, jbarnes@...tuousgeek.org,
	rdunlap@...otime.net, mtk.manpages@...il.com
Subject: Re: Multiple MSI, take 4

On Fri, 2008-07-11 at 15:16 -0600, Matthew Wilcox wrote:
> Here we go with take 4.  Changes:
> 
>  - Check the requested number of interrupts against the maximum number
>    the device claims to support.  Thanks to Hidetoshi Seto for pointing
>    out this oversight.
>  - Implemented Eric's suggestion of using a single IRQ and storing the
>    data with it.
>  - As a result, don't try to support the mode in the AHCI driver where
>    the excess ports all share the last interrupt.  It could be done, but
>    it would be rather messy and I don't have hardware that supports that
>    mode anyway.
> 
> I'm fairly comfortable with the subchannel notion we're introducing
> here.  It's more flexible than MSI and doesn't impose a penalty on
> architectures which don't implement it.  It makes some things more
> complex, but it makes other things simpler, so I think it's a wash from
> a cleanliness standpoint.

I prefer you initial approach. If those are effectively one interrupt,
you end up with the whole IRQ_INPROGRESS logic going bonkers trying to
prevent them from occuring at the same time and possibly losing some.

I think the masking "issue" is mostly a non-issue as I explained in
other emails.

Cheers,
Ben.


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