Re: [PATCH RFC 00/15] Add VFIO mediated device support and IMS support for the idxd driver.

From: Jason Gunthorpe <jgg@mellanox.com>
To: "Raj, Ashok" <ashok.raj@intel.com>
Cc: "Tian, Kevin" <kevin.tian@intel.com>,
	Alex Williamson <alex.williamson@redhat.com>,
	"Jiang, Dave" <dave.jiang@intel.com>,
	"vkoul@kernel.org" <vkoul@kernel.org>,
	"megha.dey@linux.intel.com" <megha.dey@linux.intel.com>,
	"maz@kernel.org" <maz@kernel.org>,
	"bhelgaas@google.com" <bhelgaas@google.com>,
	"rafael@kernel.org" <rafael@kernel.org>,
	"gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"hpa@zytor.com" <hpa@zytor.com>,
	"Pan, Jacob jun" <jacob.jun.pan@intel.com>,
	"Liu, Yi L" <yi.l.liu@intel.com>,
	"Lu, Baolu" <baolu.lu@intel.com>,
	"Kumar, Sanjay K" <sanjay.k.kumar@intel.com>,
	"Luck, Tony" <tony.luck@intel.com>,
	"Lin, Jing" <jing.lin@intel.com>,
	"Williams, Dan J" <dan.j.williams@intel.com>,
	"kwankhede@nvidia.com" <kwankhede@nvidia.com>,
	"eric.auger@redhat.com" <eric.auger@redhat.com>,
	"parav@mellanox.com" <parav@mellanox.com>,
	"dmaengine@vger.kernel.org" <dmaengine@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"x86@kernel.org" <x86@kernel.org>,
	"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH RFC 00/15] Add VFIO mediated device support and IMS support for the idxd driver.
Date: Sat, 9 May 2020 09:21:13 -0300	[thread overview]
Message-ID: <20200509122113.GP19158@mellanox.com> (raw)
In-Reply-To: <20200509000909.GA79981@otc-nc-03>

On Fri, May 08, 2020 at 05:09:09PM -0700, Raj, Ashok wrote:
> Hi Jason
> 
> On Fri, May 08, 2020 at 08:16:10PM -0300, Jason Gunthorpe wrote:
> > On Fri, May 08, 2020 at 01:47:10PM -0700, Raj, Ashok wrote:
> > 
> > > Even when uaccel was under development, one of the options
> > > was to use VFIO as the transport, goal was the same i.e to keep
> > > the user space have one interface. 
> > 
> > I feel a bit out of the loop here, uaccel isn't in today's kernel is
> > it? I've heard about it for a while, it sounds very similar to RDMA,
> > so I hope they took some of my advice...
> 
> I think since 5.7 maybe? drivers/misc/uacce. I don't think this is like
> RDMA, its just a plain accelerator. There is no connection management,
> memory registration or other things.. IB was my first job at Intel,
> but saying that i would be giving my age away :)

rdma was the first thing to do kernel bypass, all this stuff is like
rdma at some level.. I see this looks like the 'warp driver' stuff
redone

Wow, lots wrong here. Oh well.

> > putting emulation code back into them, except in a more dangerous
> > kernel location. This does not seem like a net win to me.
> 
> Its not a whole lot of emulation right? mdev are soft partitioned. There is
> just a single PF, but we can create a separate partition for the guest using
> PASID along with the normal BDF (RID). And exposing a consistent PCI like
> interface to user space you get everything else for free.
> 
> Yes, its not SRIOV, but giving that interface to user space via VFIO, we get 
> all of that functionality without having to reinvent a different way to do it.
> 
> vDPA went the other way, IRC, they went and put a HW implementation of what
> virtio is in hardware. So they sort of fit the model. Here the instance
> looks and feels like real hardware for the setup and control aspect.

VDPA and this are very similar, of course it depends on the exact HW
implementation.

Jason