linux-kernel - Re: [PATCH 0/6] VMD MSI Remapping Bypass

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Message-ID: <5b9074dcdfef82ab2f93ab09b635a657666b3d91.camel@intel.com>
Date:   Mon, 17 Aug 2020 16:14:17 +0000
From:   "Derrick, Jonathan" <jonathan.derrick@...el.com>
To:     "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>
CC:     "hch@....de" <hch@....de>,
        "andrzej.jakowski@...ux.intel.com" <andrzej.jakowski@...ux.intel.com>,
        "helgaas@...nel.org" <helgaas@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Kalakota, SushmaX" <sushmax.kalakota@...el.com>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH 0/6] VMD MSI Remapping Bypass

Hi Lorenzo,

On Tue, 2020-07-28 at 13:49 -0600, Jon Derrick wrote:
> The Intel Volume Management Device acts similar to a PCI-to-PCI bridge in that
> it changes downstream devices' requester-ids to its own. As VMD supports PCIe
> devices, it has its own MSI/X table and transmits child device MSI/X by
> remapping child device MSI/X and handling like a demultiplexer.
> 
> Some newer VMD devices (Icelake Server and client) have an option to bypass the
> VMD MSI/X remapping table. This allows for better performance scaling as the
> child device MSI/X won't be limited by VMD's MSI/X count and IRQ handler.
> 
> It's expected that most users don't want MSI/X remapping when they can get
> better performance without this limitation. This set includes some long overdue
> cleanup of overgrown VMD code and introduces the MSI/X remapping disable.
> 
> Applies on top of e3beca48a45b ("irqdomain/treewide: Keep firmware node
> unconditionally allocated") and ec0160891e38 ("irqdomain/treewide: Free
> firmware node after domain removal") in tip/urgent
> 
> 
> Jon Derrick (6):
>   PCI: vmd: Create physical offset helper
>   PCI: vmd: Create bus offset configuration helper
>   PCI: vmd: Create IRQ Domain configuration helper
>   PCI: vmd: Create IRQ allocation helper
>   x86/apic/msi: Use Real PCI DMA device when configuring IRTE
>   PCI: vmd: Disable MSI/X remapping when possible
> 
>  arch/x86/kernel/apic/msi.c   |   2 +-
>  drivers/pci/controller/vmd.c | 344 +++++++++++++++++++++++------------
>  2 files changed, 224 insertions(+), 122 deletions(-)
> 
> 
> base-commit: ec0160891e387f4771f953b888b1fe951398e5d9

Gentle reminder. Please don't forget about this.
We have a few more patches coming soon that I'd prefer to stage upon
this set.