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

[Dor Laor]

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