RE: [Patch v5 0/3] Introduce a driver to support host accelerated access to Microsoft Azure Blob for Azure VM

From: Long Li <longli@microsoft.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: vkuznets <vkuznets@redhat.com>,
	Bart Van Assche <bvanassche@acm.org>,
	"longli@linuxonhyperv.com" <longli@linuxonhyperv.com>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
	Jonathan Corbet <corbet@lwn.net>,
	KY Srinivasan <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	Wei Liu <wei.liu@kernel.org>, Dexuan Cui <decui@microsoft.com>,
	Bjorn Andersson <bjorn.andersson@linaro.org>,
	Hans de Goede <hdegoede@redhat.com>,
	"Williams, Dan J" <dan.j.williams@intel.com>,
	Maximilian Luz <luzmaximilian@gmail.com>,
	Mike Rapoport <rppt@kernel.org>,
	Ben Widawsky <ben.widawsky@intel.com>,
	Jiri Slaby <jirislaby@kernel.org>,
	Andra Paraschiv <andraprs@amazon.com>,
	Siddharth Gupta <sidgup@codeaurora.org>,
	Hannes Reinecke <hare@suse.de>
Subject: RE: [Patch v5 0/3] Introduce a driver to support host accelerated access to Microsoft Azure Blob for Azure VM
Date: Mon, 11 Oct 2021 19:38:54 +0000	[thread overview]
Message-ID: <BY5PR21MB1506196929D2BD0300B4388ACEB59@BY5PR21MB1506.namprd21.prod.outlook.com> (raw)
In-Reply-To: <YWR7TuGNaMJLXdVr@kroah.com>

> Subject: Re: [Patch v5 0/3] Introduce a driver to support host accelerated access
> to Microsoft Azure Blob for Azure VM
> 
> On Mon, Oct 11, 2021 at 05:46:48PM +0000, Long Li wrote:
> > > Subject: Re: [Patch v5 0/3] Introduce a driver to support host
> > > accelerated access to Microsoft Azure Blob for Azure VM
> > >
> > > Greg Kroah-Hartman <gregkh@linuxfoundation.org> writes:
> > >
> > > ...
> > > >
> > > > Not to mention the whole crazy idea of "let's implement our REST
> > > > api that used to go over a network connection over an ioctl instead!"
> > > > That's the main problem that you need to push back on here.
> > > >
> > > > What is forcing you to put all of this into the kernel in the
> > > > first place?  What's wrong with the userspace network
> > > > connection/protocol that you have today?
> > > >
> > > > Does this mean that we now have to implement all REST apis that
> > > > people dream up as ioctl interfaces over a hyperv transport?  That
> > > > would be insane.
> > >
> > > As far as I understand, the purpose of the driver is to replace a "slow"
> > > network connection to API endpoint with a "fast" transport over
> > > Vmbus. So what if instead of implementing this new driver we just
> > > use Hyper-V Vsock and move API endpoint to the host?
> >
> > Hi Vitaly,
> >
> > We looked at Hyper-V Vsock when designing this driver. The problem is that
> the Hyper-V device model of Vsock can't support the data throughput and scale
> needed for Blobs. Vsock is mostly used for management tasks.
> >
> > The usage of Blob in Azure justifies an dedicated VMBUS channel (and sub-
> channels) for a new VSP/VSC driver.
> 
> Why not just fix the vsock code to handle data better?  That way all users of it
> would benefit.

Hi Greg,

The Vsock is connection based.  On both Guest and Host, the model is around a connection over a socket. Internally, the Hyper-V creates a device for each connection. But it doesn't scale to large number of CPUs over a socket connection. Hyper-V vsock is designed to perform configuration management for a VM running on Hyper-V.

The Azure Blob service is not connection based. It doesn't fit into the device model presented by Vsock from Hyper-V.

Thanks,

Long

> 
> thanks,
> 
> greg k-h