Re: [PATCH 0/6] Adding the Android Emulator hypervisor driver accelerator

[Haitao Shan]

On Fri, Mar 3, 2023 at 9:12 AM Daniel P. Berrangé <berrange@redhat.com> wrote:
>
> On Fri, Mar 03, 2023 at 08:50:18AM -0800, Haitao Shan wrote:
> > On Fri, Mar 3, 2023 at 2:34 AM Daniel P. Berrangé <berrange@redhat.com> 
> > wrote:
> > >
> > > On Thu, Mar 02, 2023 at 06:25:59PM -0800, Haitao Shan wrote:
> > > > The Android Emulator hypervisor driver is a hypervisor for Windows (7
> > > > or later), made by porting the KVM from the linux kernel 4.9-rc7. Its
> > > > initial purpose was to support the Android Emulator on the AMD
> > > > platforms as the old name "Android Emulator Hypervisor Driver for AMD
> > > > Processors" suggested. Despite the name, Intel processors have been
> > > > supported ever since its first release. Since Intel dropped HAXM 
> > > > support,
> > > > the android emulator is switching from HAXM to AEHD.
> > >
> > > When HAXM was proposed for deprecation & removal from QEMU, the suggestion
> > > was that users should switch to Windows' native replacement WHPX, which
> > > QEMU already has support for.
> >
> > Sorry I was not aware of Intel's suggestion when HAXM was deprecated.
> > Is this a decision already, which shuts the door for any other 3rd party
> > hypervisors?
>
> No, we're always open to new proposals. It merely means that it
> might be harder to justify why the new hypervisor is a net benefit
> for QEMU, when there is a competing solution supported by the OS
> vendor.
Thanks for the clarification. It is great that the door is not shut completely.

>
> > > What is the rationale for wanting to introduce a 3rd party hypervisor
> > > solution like AEHD, for the Android emulator, rather than just sticking
> > > with the standard WHPX hypervisor available for Windows ? IIUC, the
> > > Android emulator can already support WHPX according to these pages:
> > >
> > >   https://developer.android.com/studio/run/emulator-acceleration
> > >   
> > > https://learn.microsoft.com/en-us/dotnet/maui/android/emulator/hardware-acceleration?view=net-maui-7.0
> > You are right. WHPX is supported by the android emulator. The reason for
> > supporting AEHD:
> >
> > 1. HyperV is a type-1 hypervisor, which does not coexist with other 
> > hypervisors.
> > According to our data, there are both users who have to live with HyperV on 
> > or
> > with HyperV off. Those users depend on certain Windows features (or 3rd 
> > party
> > programs) that have to turn on or turn off HyperV. Offering AEHD allows us 
> > to
> > serve both types of users. This is the major benefit. I think this
> > argument is true
> > for upstream QEMU users as well.
>
> Yes, it is an akward situation if users cannot enable use of WHPX.
> I don't have any better suggestion in that scenario.
>
> > 2. Actually, AEHD started development before WHPX was added to the android
> > emulator. But porting/writing a new hypervisor just took lots of time.
> > In the middle,
> > Microsoft offered us WHPX. It could be the case that AEHD was never started 
> > if
> > WHPX had been offered one or two years earlier. However, we decided to 
> > continue.
> > First, see reason 1. Second, at least at that time, WHPX was noticeably 
> > slower
> > than both HAXM and AEHD. Third, Microsoft clearly stated there would not be
> > any backporting of WHPX to older versions of Windows. And those using old
> > versions of Windows need a solution in addition to HAXM.
>
> FYI, from the QEMU POV, we only aim to support the two most recent major
> releases of Windows.
Just want to point out that only Windows 10 1809+ (or
perhaps 1803+) supports WHPX. And how to enable WHPX varies
among versions of Windows 11/10. For example, on Windows 11,
there is no need to explicitly enable it using the Windows Features
dialog, which is good according to my taste.

But I do agree that earlier Windows 10 versions should not be considered
as recent major releases any more nowadays.

>
> At a technical level we've set the compilation baseline to Windows 8, but
> per the support policy we only really support Windows 10 and 11 right now.
>
> > 3. Compared with HAXM, which looks like the default solution when HyperV
> > must be off, AEHD supports both Intel and AMD. And according to user 
> > feedback
> > and our own tests, AEHD can support Windows 10. This was the reason
> > why I maintained a patched QEMU ever since 4.2.0 specifically for them.
>
> Yep, no disagreement that AEHD looks more useful for HAXM given the
> cross vendor CPU support.
Oops. By saying supporting Windows 10, I really mean Windows 10 guests.

>
> > 4. Although it is called Android Emulator hypervisor driver, it has nothing 
> > that
> > is android specific. And I've seen the upstream QEMU successfully 
> > refactored the
> > accelerator logic. This made adding a new hypervisor support less intrusive 
> > to
> > the main code base. I have a good will and intention to maintain what I
> > submitted if it could be approved by the community. I hope this does
> > not place (or
> > at least place very minimum) burden on the maintainers, should it be 
> > accepted.
>
> Ok, thank you.
>
> I don't have any specific requests / suggestion myself, but I see others
> replied wondering whether there's any sense is sharing code with the
> KVM driver in QEMU. Hopefully the QEMU KVM maintainers will comment with
> their views on the matter.
>
> With regards,
> Daniel
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>


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Haitao @Google