Cloud product kernel requirements

[Kyle Mestery (kmestery)]

On Oct 30, 2013, at 9:38 AM, Daniel P. Berrange <berrange at redhat.com> wrote:
> On Wed, Oct 30, 2013 at 10:07:46AM -0400, Josh Boyer wrote:
>> Hi All,
>> 
>> I realize the WG is just forming up and you have a lot of other items
>> to cover for now, but I wanted to get this sent out and have people
>> start thinking about it sooner rather than later.
>> 
>> The kernel team has heard in the past that the Cloud group would like
>> to see something of a more minimal kernel for usage in cloud images.
>> We'd like to hear the requirements for what this smaller image would
>> need to cover.
>> 
>> Right now, a default x86_64 kernel package on f20 is ~134MB installed.
>> Most of that is device drivers installed in /lib/modules/`uname -r`/.
>> The vmlinux binary is about 5MB and the initramfs (which is created
>> at install time and can actually vary quite widely depending on
>> various things) is about 11MB.  Drivers can be trimmed to a degree,
>> but please keep in mind that the kernel is already relatively small
>> for the functionality it provides.  For example, it is not much bigger
>> than glibc-common (119MB).
>> 
>> So, some caveats to keep in mind while you're thinking about this:
>> 
>> 1) We're mostly talking about packaging here, not building a separate
>> cloud kernel package or vmlinux.  The kernel team really wants to have
>> a single vmlinux across the 3 products if at all possible.  We can't
>> scale to much else.
>> 
>> 2) What usecases is the cloud image going to cover?  E.g. is it just
>> virtio stuff, or will it also fit PCI passthru (which then requires
>> drivers for those PCI devices)?
> 
> FWIW, OpenStack cloud now supports use of PCI passthrough for guests,
> so looking at the most general cloud case, we can't remove all the
> non-virtio stuff. Most common PCI passthrough usage will likely be
> for SRIOV NIC devices, with others more niche use-cases.
> 
I second Daniel's comments here. In fact, in Icehouse the PCI
passthrough support is likely to get better, there is a lot of interest
for this especially in the NFV area. NICs are the most likely area of
interest here, but I know Intel was also interested in graphics devices
and passthrough as well.

Thanks,
Kyle

>> 3) What are the common
>> provisioning requirements that are driving the
>> size reduction?  (See comment about glibc-common.  I would think
>> change is needed in multiple packages, not just the kernel.)
>> 
>> 4) Other "cloudy" stuff that I'm entirely unaware of that might be
>> relevant.  Explain it to me like I'm a child.
> 
> Does anyone have an accurate report on where physical space in the
> current cloud image goes to ? Just doing a 'du' on the cloud image
> is only giving logical disk space, which doesn't correspond directly
> to physical image space, due to differing compression ratios for
> different types of content.
> 
> Daniel