[libvirt PATCH] ci: maximize cirrus CI ram/cpu allocation

[Daniel P. Berrangé]

On Wed, Jul 21, 2021 at 06:39:07AM -0400, Andrea Bolognani wrote:
> On Tue, Jul 20, 2021 at 04:05:22PM +0100, Daniel P. Berrangé wrote:
> > For macOS you always get the maximum configuration by default (12 CPUs,
> > 24 GB RAM), but for FreeBSD you get 2 CPUs, 4 GBs by default. This
> > change increases the allocation to 8 CPUs, 8 GBs for FreeBSD.
> >
> > ---
> > In theory this could make builds quicker. In practice I've not been
> > able to measure a difference due to large variance between runs.
> 
> Should we actually do this? The fact that FreeBSD builds take so much
> time is painful, but if you haven't been able to measure significant
> improvements from maximizing the number of CPUs assigned to the VM
> then perhaps other factors such as slow disk speed are to blame
> instead. In fact, looking at recent jobs it looks like they mostly
> fall in line with Linux builds...

Yeah, I'm in two minds and just sent this patch to get a second
opinion.

I noticed the ability to configure this when switching QEMU to
use lcitool for generating the freebsd/macos configuration.
The increase in resources for FreeBSD VMs made a significant
difference to QEMU build times - the difference between passing
and hitting the job limit timeout.

Thus I'm really puzzelled why libvirt didn't see a real benefit
when I tested it.  As you say though, FreeBSD builds are no worse
than Linux builds, so it isn't critical for us.

> We certainly don't need 24 GiB of RAM to build libvirt, and grabbing
> 12 CPUs seems excessively greedy too. Can we try being nice citizens
> instead, and allocate something like 4 CPUs and 2 GiB of RAM across
> the board? I expect that the resulting build times would still be
> close to what we're seeing for containerized Linux builds, and so the
> overall pipeline completion time won't be negatively affected.

FWIW, for macOS systems you get the maximum resources no matter what,
as they always allocate you an entire system. I presume this is
because macOS builders run on physical hardware due to macOS license
rules preventing VM usages.

Regards,
Daniel
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