linux-kernel - Re: Configure MSI-X vectors to target different CPUs

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Date:	Thu, 21 Feb 2008 21:59:14 -0600
From:	Robert Hancock <hancockr@...w.ca>
To:	caiying@...oo.com
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Configure MSI-X vectors to target different CPUs

caiying@...oo.com wrote:
> Hi,
> 
> In MSI-HOWTO, it's said:
> 
> "Using MSI enables the device functions to support two or more vectors, which can be configured to target different CPUs to increase scalability."
> 
> So how can I set up MSI-X vectors to target different CPUs? I want to allocate the same number of MSI-X vectors as CPUs, and equally distribute them to every CPU.
> 
> Is it automatically done by Linux when I call pci_enable_msix()? If yes, how? If not, what should I do? My guess is to set the affinity of the interrupts manually. Am I right?
> 
> Please CC'ed me (caiying@...oo.com) answers/comments  in response to this posting. 
> 
> Thanks,
> Ying

If the device actually supports multiple vectors (not all do), I think 
they should show up as separate interrupts in /proc/interrupts and you 
can either set the affinity manually, or maybe irqbalance is smart 
enough for this.

Careful, though, as in some cases this may reduce performance due to 
causing more cache line bouncing between CPUs.
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