AHCI?

AHCI?

[tsuraan]

Is there any plan to add AHCI support to kvm?  It seems like it would
be an ideal alternative to the LSI SCSI driver, since AHCI is
supported by 64-bit Solaris as well as nearly every other modern OS.

Re: AHCI?

[Avi Kivity]

tsuraan wrote:
> Is there any plan to add AHCI support to kvm?  It seems like it would
> be an ideal alternative to the LSI SCSI driver, since AHCI is
> supported by 64-bit Solaris as well as nearly every other modern OS.
>   

No plan that I know of.  Is the LSI scsi device not supported by Solaris?

-- 
error compiling committee.c: too many arguments to function

Re: AHCI?

[tsuraan]

> No plan that I know of.  Is the LSI scsi device not supported by Solaris?

Yeah, there was a short thread about it last July
(http://www.mail-archive.com/kvm@vger.kernel.org/msg01633.html).  The
jist of it is that 64-bit OpenSolaris no longer supports the 53c895a
SCSI controller.  According to that thread, the 53c1010 is what VMWare
uses, and OpenSolaris still uses that.

I don't really understand how a VM exposes a virtual device to a
hosted OS, but I assume that it involves looking at a driver for a
piece of hardware and then writing some code that emulates the
behaviour expected by that driver?  I would think AHCI would be a
great way to go, if that's the case, since it would be an actual
implementation of a standard instead of an arbitrary card.  Does kvm
use the qemu source for its drivers, or is there a separate source
tree for it now?  I could at least have a look at the LSI driver so I
have some idea what I'm talking about...

Re: AHCI?

[Avi Kivity]

tsuraan wrote:
>> No plan that I know of.  Is the LSI scsi device not supported by Solaris?
>>     
>
> Yeah, there was a short thread about it last July
> (http://www.mail-archive.com/kvm@vger.kernel.org/msg01633.html).  The
> jist of it is that 64-bit OpenSolaris no longer supports the 53c895a
> SCSI controller.  According to that thread, the 53c1010 is what VMWare
> uses, and OpenSolaris still uses that.
>
>   

I see.  That sucks.

> I don't really understand how a VM exposes a virtual device to a
> hosted OS, but I assume that it involves looking at a driver for a
> piece of hardware and then writing some code that emulates the
> behaviour expected by that driver?  

The best way is to look at the device spec and write the emulation to 
conform to that.

> I would think AHCI would be a
> great way to go, if that's the case, since it would be an actual
> implementation of a standard instead of an arbitrary card.  Does kvm
> use the qemu source for its drivers, or is there a separate source
> tree for it now?  

We use the qemu source (we have our own branch, but it's very close to 
qemu upstream).


-- 
error compiling committee.c: too many arguments to function

Re: AHCI?

[tsuraan]

> I see.  That sucks.

Yeah...  Is there any reason that kvm is hard-coded to only allow 4
IDE devices? Is it an issue with the BIOS implementation, or is it
just a random limit?  If there's some macro somewhere that defines
NUM_IDE to 2, and I could change that to 5, then I'd be perfectly
happy; I don't really care about SCSI vs. IDE, I just want to be able
to use 9 drives with kvm instead of the 4 that I'm currently able to
access.

Re: AHCI?

[Avi Kivity]

tsuraan wrote:
>> I see.  That sucks.
>>     
>
> Yeah...  Is there any reason that kvm is hard-coded to only allow 4
> IDE devices? Is it an issue with the BIOS implementation, or is it
> just a random limit?  If there's some macro somewhere that defines
> NUM_IDE to 2, and I could change that to 5, then I'd be perfectly
> happy; I don't really care about SCSI vs. IDE, I just want to be able
> to use 9 drives with kvm instead of the 4 that I'm currently able to
> access.
>   

If you want that and good performance too write a virtio driver, and use 
virtio disk instead of IDE or SCSI.

I don't think the IDE implementation in qemu supports more than four 
disks, that's an IDE limitation.  No doubt it could be worked around by 
adding more IDE controllers, it's probably not a lot of code but quite 
tricky.


-- 
error compiling committee.c: too many arguments to function

Re: AHCI?

[tsuraan]

> If you want that and good performance too write a virtio driver, and use
> virtio disk instead of IDE or SCSI.

Is there a place where the interface types are documented?  The man
page lists ide, scsi, sd, mtd, floppy, pflash, and virtio.  There's a
virtio page on the kvm wiki, and I think I can guess what ide, scsi,
and floppy are, but where are the rest of them documented?  I'm going
through the list right now looking for a combination that will let
solaris see all my disks, but a more informed approach might be more
productive.

> I don't think the IDE implementation in qemu supports more than four
> disks, that's an IDE limitation.  No doubt it could be worked around by
> adding more IDE controllers, it's probably not a lot of code but quite
> tricky.

So it's down to hacking the VM code or writing a solaris driver.  Fun :)