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

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Date:	Fri, 25 May 2007 13:16:57 -0700
From:	Jonathan Lundell <linux@...dell-bros.com>
To:	Andi Kleen <ak@...e.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Jay Cliburn <jacliburn@...lsouth.net>,
	Grzegorz Krzystek <ninex@...ex.eu.org>, 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 May 24, 2007, at 10:51 PM, Andi Kleen wrote:

>> 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?
>
> At least on 10GB ethernet it is a significant difference; you usually
> cannot go anywhere near line speed without MSI
>
> I suspect it is visible on high performance / multiple GB NICs too.

Why would that be? As the packet rate goes up and NAPI polling kicks  
in, wouldn't MSI make less and less difference?

I like the fact that MSI gives us finer control over CPU affinity  
than many INTx implementations, but that's a different issue.

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