Re: Better qemu/kvm defaults (was Re: [RFC PATCH 0/4] Gang scheduling in CFS)

[Avi Kivity <avi@redhat.com>]

On 12/29/2011 06:07 PM, Dor Laor wrote:
> On 12/26/2011 11:05 AM, Avi Kivity wrote:
>> On 12/26/2011 05:14 AM, Nikunj A Dadhania wrote:
>>>>
>>>> btw you can get an additional speedup by enabling x2apic, for
>>>> default_send_IPI_mask_logical().
>>>>
>>> In the host?
>>>
>>
>> In the host, for the guest:
>>
>>   qemu -cpu ...,+x2apic
>>
>
> It seems to me that we should improve our default flags.
> So many times users fail to submit the proper huge command-line
> options that we require. Honestly, we can't blame them, there are so
> many flags and so many use cases its just too hard to get it right for
> humans.
>
> I propose a basic idea and folks are welcome to discuss it:
>
> 1. Improve qemu/kvm defaults
>    Break the current backward compatibility (but add a --default-
>    backward-compat-mode)

This exists, -M pc-1.0.

> and set better values for:
>     - rtc slew time
>     - cache=none
>     - x2apic, maybe enhance qemu64 or move to -cpu host?

We tried this for 1.0, but it caused regressions.  Need to try again for
1.1.

>     - aio=native|threads (auto-sense?)
>     - use virtio devices by default

Can't install non-Linux guests.

>     - more?
>
>    Different defaults may be picked automatically when TCG|KVM used.


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