linux-kernel - Re: [PATCH 1/2] msi: Invert the sense of the MSI enables.

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Message-Id: <20070524213157.1d39458f.akpm@linux-foundation.org>
Date:	Thu, 24 May 2007 21:31:57 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	ebiederm@...ssion.com (Eric W. Biederman)
Cc:	Greg Kroah-Hartman <gregkh@...e.de>,
	Jay Cliburn <jacliburn@...lsouth.net>,
	Grzegorz Krzystek <ninex@...eX.eu.org>,
	Andi Kleen <ak@...e.de>, ninex@...pl,
	<linux-kernel@...r.kernel.org>,
	<linux-pci@...ey.karlin.mff.cuni.cz>,
	Michael Ellerman <michael@...erman.id.au>,
	David Miller <davem@...emloft.net>,
	Tony Luck <tony.luck@...el.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 1/2] msi: Invert the sense of the MSI enables.

On Thu, 24 May 2007 22:19:09 -0600 ebiederm@...ssion.com (Eric W. Biederman) wrote:

> Currently we blacklist known bad msi configurations which means we
> keep getting MSI enabled on chipsets that either do not support MSI,
> or MSI is implemented improperly.  Since the normal IRQ routing
> mechanism seems to works even when MSI does not, this is a bad default
> and causes non-functioning systems for no good reason.
> 
> So this patch inverts the sense of the MSI bus flag to only enable
> MSI on known good systems.  I am seeding that list with the set of
> chipsets with an enabled hypertransport MSI mapping capability.  Which
> is as close as I can come to an generic MSI enable.  So for actually
> using MSI this patch is a regression, but for just having MSI enabled
> in the kernel by default things should just work with this patch
> applied.
> 
> People can still enable MSI on a per bus level for testing by writing
> to sysfs so discovering chipsets that actually work (assuming we are
> using modular drivers) should be pretty straight forward.

Yup.

Do we have a feel for how much performace we're losing on those 
systems which _could_ do MSI, but which will end up defaulting
to not using it?
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