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Re: Recommended features to enable after --without-default-features?


From: Alex Bennée
Subject: Re: Recommended features to enable after --without-default-features?
Date: Fri, 01 Jul 2022 11:59:23 +0100
User-agent: mu4e 1.7.27; emacs 28.1.90

"Anders Pitman" <anders@apitman.com> writes:

> I'm using QEMU to run microvms and want to remove as many unnecessary options 
> as possible. Currently the following appears to be
> sufficient for running my VMs:
>
> ./configure \
>         --without-default-features \
>         --enable-kvm \
>         --enable-slirp \
>         --target-list=x86_64-softmmu
>
> Looking through the list of options though, I'm wondering if any of them are 
> highly recommended to enable?
>
> For example maybe avx2, avx512f, numa, nvmm, the various vhost-* options, etc?
>
> It's hard for me to guess where where each feature is used in the
> codebase and whether it will affect performance or functionality.

The default features are default for a reason. Unless you specifically
know what you want to build then I would stick to them. Also default
features are still only enabled if you have the supporting development
libraries installed so your build is likely not the fullest fat it can
be.

A lot of the (static) memory usage comes down to additional machine and
device models so you can create an alternative to
configs/devices/i386-softmmu/default.mk and use
--with-devices-x86_64=/path/to/mk which only for example contains
CONFIG_MICROVM=y.

However these are both considered expert options for those familiar with
how QEMU is put together.

>
> Thanks,
> //anders


-- 
Alex Bennée



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