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

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Date:   Mon, 11 Oct 2021 17:57:04 +0000
From:   Long Li <longli@...rosoft.com>
To:     vkuznets <vkuznets@...hat.com>
CC:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Bart Van Assche <bvanassche@....org>,
        "longli@...uxonhyperv.com" <longli@...uxonhyperv.com>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Hans de Goede <hdegoede@...hat.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        Maximilian Luz <luzmaximilian@...il.com>,
        Mike Rapoport <rppt@...nel.org>,
        Ben Widawsky <ben.widawsky@...el.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        Andra Paraschiv <andraprs@...zon.com>,
        Siddharth Gupta <sidgup@...eaurora.org>,
        Hannes Reinecke <hare@...e.de>
Subject: RE: [Patch v5 0/3] Introduce a driver to support host accelerated
 access to Microsoft Azure Blob for Azure VM

> 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@...uxfoundation.org> writes:
> 
> > On Fri, Oct 08, 2021 at 01:11:02PM +0200, Vitaly Kuznetsov wrote:
> >> Greg Kroah-Hartman <gregkh@...uxfoundation.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.
> >
> > Given that the network connection is already over vmbus, how is this
> > "slow" today?  I have yet to see any benchmark numbers anywhere :(
> >
> >> So what if instead of implementing this new driver we just use
> >> Hyper-V Vsock and move API endpoint to the host?
> >
> > What is running on the host in the hypervisor that is supposed to be
> > handling these requests?  Isn't that really on some other guest?
> >
> 
> Long,
> 
> would it be possible to draw a simple picture for us describing the backend flow
> of the feature, both with network connection and with this new driver? We're
> struggling to understand which particular bottleneck the driver is trying to
> eliminate.

Thank you for this great suggestion. I'm preparing some diagrams for describing the problem. I will be sending them soon.

Thanks,

Long

> 
> --
> Vitaly