linux-kernel - Re: [PATCH v2 03/10] PCI/LUO: Forward prepare()/freeze()/cancel() callbacks to driver

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Message-ID: <CALzav=edEDvz98KKtmMLWcW33PgE4aTy6K7YLSK0_jx1PdRqBw@mail.gmail.com>
Date: Fri, 3 Oct 2025 11:27:44 -0700
From: David Matlack <dmatlack@...gle.com>
To: Chris Li <chrisl@...nel.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Bjorn Helgaas <bhelgaas@...gle.com>, 
	"Rafael J. Wysocki" <rafael@...nel.org>, Danilo Krummrich <dakr@...nel.org>, Len Brown <lenb@...nel.org>, 
	Pasha Tatashin <pasha.tatashin@...een.com>, linux-kernel@...r.kernel.org, 
	linux-pci@...r.kernel.org, linux-acpi@...r.kernel.org, 
	Pasha Tatashin <tatashin@...gle.com>, Jason Miu <jasonmiu@...gle.com>, 
	Vipin Sharma <vipinsh@...gle.com>, Saeed Mahameed <saeedm@...dia.com>, 
	Adithya Jayachandran <ajayachandra@...dia.com>, Parav Pandit <parav@...dia.com>, William Tu <witu@...dia.com>, 
	Mike Rapoport <rppt@...nel.org>, Jason Gunthorpe <jgg@...pe.ca>, Leon Romanovsky <leon@...nel.org>
Subject: Re: [PATCH v2 03/10] PCI/LUO: Forward prepare()/freeze()/cancel()
 callbacks to driver

On Fri, Oct 3, 2025 at 10:49 AM Chris Li <chrisl@...nel.org> wrote:
>
> On Fri, Oct 3, 2025 at 5:26 AM Greg Kroah-Hartman
> <gregkh@...uxfoundation.org> wrote:
> >
> > On Fri, Oct 03, 2025 at 12:26:01AM -0700, Chris Li wrote:
> >
> > > It is more than just one driver, we have vfio-pci, idpf, pci-pf-stub
> > > and possible nvme driver.
> >
> > Why is nvme considered a "GPU" that needs context saved?
>
> NVME is not a GPU. The internal reason to have NVME participate in the
> liveupdate is because the NVME shutdown of the IO queue is very slow,
> it contributes the largest chunk of delay in the black out window for
> liveupdate. The NVME participation is just an optimization to avoid
> resetting the NVME queue. Consider it as (optional ) speed
> optimization.

This is not true. We haven't made any changes to the nvme driver
within Google for Live Update.

The reason I mentioned nvme in another email chain is because Google
has some hosts where we want to preserve VFs bound to vfio-pci across
Live Update where the PF is bound to nvme. But Jason is suggesting we
seriously explore switching the PF driver to vfio-pci before trying to
upstream nvme support for Live Update, which I think is fair.