CentOS 7 host with 22.04 LTS guest slow

[Ralf Mardorf]

On Tue, 2022-09-27 at 08:05 +0200, Ralf Mardorf wrote:
> On Mon, 2022-09-26 at 21:14 +0100, Colin Law wrote:
> > On Mon, 26 Sep 2022, 21:06 Jerry Geis, <jerry.geis at gmail.com> wrote:
> > 
> > >  I am surprised that my "appearance" of disk speed like compile time
> > > is not faster.
> > 
> > If using a faster disc has not speeded it up then that suggests that
> > disc access is not the dominant factor. When you are building, what
> > does `top` show? Perhaps it is processor speed that is the limiting
> > factor.
> 
> My machine has got a quite weak Intel Celeron dual-core CPU G1840,
> 2.80GHz. There's no noticeable difference between building something by
> using a default 7.6G (half of the RAM) tmpfs or a SATA 6GBit/s SSD ext4
> partition. IIRC there is _no_ significant difference when using a HDD,
> too. With half of the RAM I was already able to use tmpfs for almost
> everything, e.g. even a bloated kernel, but not a bloated web browser.
> The issue with tmpfs is, that it not only can run out of free space. It
> can also run out of inodes, while enough free space is still available.
> However, in almost all cases it doesn't make sense to use a HDD, SATA
> SSD or NVMe, even with a small memory. With your 128G RAM large memory,
> consider trying to build everything using tmpfs instead of a disk. For
> what else do you have got such an oversized large RAM, if not for
> intensive tmpfs usage?

PS: If you build software using a clean chroot environment, you could
even move the environment (including all the libs) to tmpfs. This is
something I haven't done myself. Last week building the python2 package
against my regular Arch Linux install failed with a core dump. I needed
to build it in a clean Arch Linux chroot, but due to my limited amount
of RAM, the chroot environment was on a SSD.
I don't know, if Ubuntu provides a feature to build Ubuntu packages in a
minimal Ubuntu chroot, just providing all build tools and the required
build dependencies for a dedicated package. It most likely does, since
when building packages for repositories, this kind of care is required.
When building only for personal usage on a single machine, it's most of
the times ok to build against the machines environment. Excepted of
building the python2 package, I don't remember that I ever used a clean
chroot environment to build my private packages. IIRC I've never done
this for Ubuntu and IIRC it's the first time I've done this for Arch
Linux.