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

[Dor Laor <dlaor@redhat.com>]

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) and set better values for:
     - rtc slew time
     - cache=none
     - x2apic, maybe enhance qemu64 or move to -cpu host?
     - aio=native|threads (auto-sense?)
     - use virtio devices by default
     - more?

    Different defaults may be picked automatically when TCG|KVM used.

2. External hardening configuration file kept in qemu.git
    For non qemu/kvm specific definitions like the io scheduler we
    should maintain a script in our tree that sets/sense the optimal
    settings of the host kernel (maybe similar one for the guest).

HTH,
Dor