Re: [Qemu-devel] Anyone seeing huge slowdown launching qemu with Linux 2.6.35?

[Avi Kivity]

 On 08/04/2010 08:27 PM, Alexander Graf wrote:
> > Well, it isn't.  Two external projects already use it.  You can't change it due 
> > to the needs to live migrate from older versions.
> You can always extend it. You can even break it with a new -M.

Yes.  But it's a pain to make sure it all works out.  We're already 
suffering from this where we have no choice, why do it where we have a 
choice?

> > It's not wrong in itself, but using it with supersized initrds is wrong.  The 
> > data is stored in qemu, host pagecache, and the guest, so three copies, it's 
> > limited by guest RAM, has to be live migrated.  Sure we could optimize it, but 
> > it's better to spend our efforts on more mainstream users.
> It's only stored twice. The host pagecache copy is gone during the lifetime of 
> the VM.

It has still evicted some other pagecache.  Footprint is footprint.  
300MB to cat some file in a guest.

> Migration also doesn't make sense for most -kernel/-initrd use cases.

You're just inviting a bug report here.  If we add a feature, let's make 
it work.

> And it's awesome for fast prototyping. Of course, once that fast becomes dog 
> slow, it's not useful anymore.

For the Nth time, it's only slow with 100MB initrds.

> I bet within the time everybody spent on this thread we would have a working 
> and stable DMA fw_cfg interface plus extra spare time for supporting breakage 
> already.

The time would have been better spent improving kvm's pio or porting 
libguestfs to use a cdrom.  I'm also hoping to get the point across that 
adding pv interfaces like crazy is not sustainable.

--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.