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

[Haitao Shan]

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?

>
> 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.

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.

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.

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.

Hope this can answer your questions. Thanks!

>
> With regards,
> Daniel
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>


-- 
Haitao @Google