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

[Alexander Graf]

On 04.08.2010, at 19:53, Anthony Liguori wrote:

> On 08/04/2010 12:37 PM, Avi Kivity wrote:
>> On 08/04/2010 08:27 PM, Anthony Liguori wrote:
>>> On 08/04/2010 12:19 PM, Avi Kivity wrote:
>>>> On 08/04/2010 08:01 PM, Paolo Bonzini wrote:
>>>>> 
>>>>> That's another story and I totally agree here, but not reusing /dev/sd* 
>>>>> is not intrinsic in the design of virtio-blk (and one thing that Windows 
>>>>> gets right; everything is SCSI, period).
>>>>> 
>>>> 
>>>> I don't really get why everything must be SCSI.  Everything must support 
>>>> read, write, a few other commands, and a large set of optional commands.  
>>>> But why map them all to SCSI?  What's the magic?
>>> 
>>> Because that's what real hardware with only a few rare exceptions.
>>> 
>> 
>> I thought that IDE was emulated as SCSI even when it wasn't.  But I guess 
>> now with SATA you're right.
> 
> IDE -> EIDE -> ATA -> SATA
> 
> ATA can encapsulate SCSI commands via ATAPI which gives you the ability to 
> have ATA based CD-ROMs among other things.
> 
> I don't believe that SATA actually uses SCSI commands for read/write 
> operations

It doesn't. In fact, it's basically just a wrapper around the normal ATA 
commands - even for read/write. Plus some additional SATA only commands for 
parallel read/write.

> but I think Linux exposes SATA drivers as SCSI anyway.

Yup. That's what libata does. Even works with PATA drives. But this is a purely 
Linux internal thing.


Alex