linux-kernel - Re: [PATCH] PCI/ASPM: Enable ASPM for links under VMD domain

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Date:   Thu, 27 Aug 2020 17:23:33 +0100
From:   "hch@...radead.org" <hch@...radead.org>
To:     "Derrick, Jonathan" <jonathan.derrick@...el.com>
Cc:     "hch@...radead.org" <hch@...radead.org>,
        "wangxiongfeng2@...wei.com" <wangxiongfeng2@...wei.com>,
        "kw@...ux.com" <kw@...ux.com>,
        "hkallweit1@...il.com" <hkallweit1@...il.com>,
        "kai.heng.feng@...onical.com" <kai.heng.feng@...onical.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mika.westerberg@...ux.intel.com" <mika.westerberg@...ux.intel.com>,
        "Mario.Limonciello@...l.com" <Mario.Limonciello@...l.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "Huffman, Amber" <amber.huffman@...el.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH] PCI/ASPM: Enable ASPM for links under VMD domain

On Thu, Aug 27, 2020 at 04:13:44PM +0000, Derrick, Jonathan wrote:
> On Thu, 2020-08-27 at 06:34 +0000, hch@...radead.org wrote:
> > On Wed, Aug 26, 2020 at 09:43:27PM +0000, Derrick, Jonathan wrote:
> > > Feel free to review my set to disable the MSI remapping which will
> > > make
> > > it perform as well as direct-attached:
> > > 
> > > https://patchwork.kernel.org/project/linux-pci/list/?series=325681
> > 
> > So that then we have to deal with your schemes to make individual
> > device direct assignment work in a convoluted way?
> 
> That's not the intent of that patchset -at all-. It was to address the
> performance bottlenecks with VMD that you constantly complain about. 

I know.  But once we fix that bottleneck we fix the next issue,
then to tackle the next.  While at the same time VMD brings zero
actual benefits.

> > Please just give us
> > a disable nob for VMD, which solves _all_ these problems without
> > adding
> > any.
> 
> I don't see the purpose of this line of discussion. VMD has been in the
> kernel for 5 years. We are constantly working on better support.

Please just work with the platform people to allow the host to disable
VMD.  That is the only really useful value add here.