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Re: [Qemu-devel] Turning off default storage devices?
From: |
Markus Armbruster |
Subject: |
Re: [Qemu-devel] Turning off default storage devices? |
Date: |
Mon, 14 Apr 2014 10:15:01 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.2 (gnu/linux) |
Peter Crosthwaite <address@hidden> writes:
> Hi Andy,
>
> On Thu, Apr 10, 2014 at 5:55 AM, Andy Lutomirski <address@hidden> wrote:
>> Currently, -M q35 boots linux quite a bit slower than the default
>> machine type. This seems to be because it takes a few hundred ms to
>> determine that there's nothing attached to the AHCI controller.
>>
>> In virtio setups, there will probably never be anything attached to
>> the AHCI controller. Would it be possible to add something like
>> -machine default_storage=off to turn off default storage devices?
>> This could include the AHCI on q35 and the cdrom and such on pc.
>>
>> There's precedent: -machine usb=off turns off the default USB
>> controllers, which is great for setups that use xhci.
>>
>
> Is there a more generic solution to your problem? Can you implement
> command line device removal in a non specific way and avoid having to
> invent AHCI or even "storage" specific arguments. You could
> considering bringing the xhci use case you mentioned under the same
> umbrella.
USB has always been off by default, at least for the boards I'm familiar
with, due to the USB emulation's non-trivial CPU use.
There's no such thing as a Q35 board without USB in the physical world.
Can't stop us from making a virtual one, of course.
Likewise, there's no such thing as a Q35 board without AHCI in the
physical world, and again that can't stop us from making a virtual one.
The difference to USB is that our q35 machines have always had AHCI even
with -nodefaults. You seem to propose adding a switch to disable AHCI,
yet leave it enabled with -nodefaults.
-nodefaults should give you a board with all the optional components
suppressed.
On the one hand, I'd rather not add exceptions to -nodefaults "give me
the board with all its optional components suppressed" semantics.
On the other hand, a few hundred ms are a long time.