Re: [Qemu-devel] Slow kernel/initrd loading via fw_cfg; Was Re: Hack integrating SeaBios / LinuxBoot option rom with QEMU trace backends

[Anthony Liguori <anthony@codemonkey.ws>]

On 10/11/2011 08:45 AM, Avi Kivity wrote:
> On 10/11/2011 03:29 PM, Anthony Liguori wrote:
>> On 10/11/2011 08:23 AM, Avi Kivity wrote:
>>> On 10/11/2011 03:19 PM, Anthony Liguori wrote:
>>>>> No, DMA has a lot bigger granularities in kvm/user interaction. We
>>>>> can easily DMA a 50MB region with a single kvm/user exit. For PIO we
>>>>> can at most do page granularity.
>>>>
>>>>
>>>> So make a proper PCI device for kernel loading.  It's a much more
>>>> natural approach and let's use alias -kernel/-initrd/-append to
>>>> -device kernel-pci,kernel=PATH,initrd=PATH
>>>
>>> This is overkill.  First let's optimize rep/movs before introducing any
>>> more interfaces.  If that doesn't work, then we can have a dma interface
>>> for fwcfg.  But a new pci device?
>>
>> This is how it would work on bare metal.  Why is a PCI device overkill
>> compared to a dma interface for fwcfg?
>>
>
> Because it's a limited use case, despite all the talk around it.
>
>> If we're adding dma to fwcfg, then fwcfg has become far too complex
>> for it's intended purpose.
>>
>
> I have to agree to that.
>
> btw, -net nic,model=virtio -net user is an internal DMA interface we
> already have.  We can boot from it. Why not use it?

tftp over slirp is probably slower than fwcfg.  It's been every time I looked.

Regards,

Anthony Liguori

>