netdev - Re: [PATCH v10 vfio 4/7] vfio/pds: Add VFIO live migration support

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Message-ID: <ZJL6wHiXHc1eBj/R@nvidia.com>
Date: Wed, 21 Jun 2023 10:27:28 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: "Tian, Kevin" <kevin.tian@...el.com>
Cc: Brett Creeley <brett.creeley@....com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"alex.williamson@...hat.com" <alex.williamson@...hat.com>,
	"yishaih@...dia.com" <yishaih@...dia.com>,
	"shameerali.kolothum.thodi@...wei.com" <shameerali.kolothum.thodi@...wei.com>,
	"shannon.nelson@....com" <shannon.nelson@....com>
Subject: Re: [PATCH v10 vfio 4/7] vfio/pds: Add VFIO live migration support

On Wed, Jun 21, 2023 at 06:49:12AM +0000, Tian, Kevin wrote:

> What is the criteria for 'reasonable'? How does CSPs judge that such
> device can guarantee a *reliable* reasonable window so live migration
> can be enabled in the production environment?

The CSP needs to work with the device vendor to understand how it fits
into their system, I don't see how we can externalize this kind of
detail in a general way.
 
> I'm afraid that we are hiding a non-deterministic factor in current protocol.

Yes

> But still I don't think it's a good situation where the user has ZERO
> knowledge about the non-negligible time in the stopping path...

In any sane device design this will be a small period of time. These
timeouts should be to protect against a device that has gone wild.

Jason