linux-kernel - Re: [RFC PATCHv2] x86/pci: Initial commit for new VMD device driver

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Date:	Mon, 5 Oct 2015 14:34:01 +0000 (UTC)
From:	Keith Busch <keith.busch@...el.com>
To:	Ingo Molnar <mingo@...nel.org>
cc:	Keith Busch <keith.busch@...el.com>,
	LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
	linux-pci@...r.kernel.org, Jiang Liu <jiang.liu@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Dan Williams <dan.j.williams@...el.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Bryan Veal <bryan.e.veal@...el.com>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [RFC PATCHv2] x86/pci: Initial commit for new VMD device
 driver

On Sat, 3 Oct 2015, Ingo Molnar wrote:
> * Keith Busch <keith.busch@...el.com> wrote:
>> +config VMDDEV
>> +	depends on PCI && PCI_DOMAINS && PCI_MSI && GENERIC_MSI_IRQ_DOMAIN && IRQ_DOMAIN_HIERARCHY
>> +	tristate "Volume Management Device Driver"
>> +	default N
>> +	select HAVE_VMDDEV
>> +	---help---
>> +	Adds support for the Intel Volume Manage Device (VMD). VMD is
>> +	a secondary PCI host bridge that allows PCI Express root ports,
>> +	and devices attached to them, to be removed from the default PCI
>> +	domain and placed within the VMD domain. If your system provides
>> +	one of these and has devices attached to it, say "Y".
>
> So what this text does not explain is why does the user care? What tangible
> benefits does this feature offer to users?

Hi Ingo,

The immediate benefit is that devices on VMD domains do not use resources
on the default PCI domain, so we have more than the 256 buses available.
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