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

[Anthony Liguori <anthony@codemonkey.ws>]

On 08/03/2010 02:05 PM, Gleb Natapov wrote:
> On Tue, Aug 03, 2010 at 09:43:39PM +0300, Avi Kivity wrote:
>    
>>> If Richard is willing to do the work to make -kernel perform
>>> faster in such a way that it fits into the overall mission of what
>>> we're building, then I see no reason to reject it.  The criteria
>>> for evaluating a patch should only depend on how it affects other
>>> areas of qemu and whether it impacts overall usability.
>>>        
>> That's true, but extending fwcfg doesn't fit into the overall
>> picture well.  We have well defined interfaces for pushing data into
>> a guest: virtio-serial (dma upload), virtio-blk (adds demand
>> paging), and virtio-p9fs (no image needed).  Adapting libguestfs to
>> use one of these is a better move than adding yet another interface.
>>
>>      
> +1. I already proposed that. Nobody objects against fast fast
> communication channel between guest and host. In fact we have one:
> virtio-serial. Of course it is much easier to hack dma semantic into
> fw_cfg interface than add virtio-serial to seabios, but it doesn't make
> it right. Does virtio-serial has to be exposed as PCI to a guest or can
> we expose it as ISA device too in case someone want to use -kernel option
> but do not see additional PCI device in a guest?
>    

fw_cfg has to be available pretty early on so relying on a PCI device 
isn't reasonable.  Having dual interfaces seems wasteful.

We're already doing bulk data transfer over fw_cfg as we need to do it 
to transfer roms and potentially a boot splash.  Even outside of loading 
an initrd, the performance is going to start to matter with a large 
number of devices.

Regards,

Anthony Liguori

> --
> 			Gleb.
>