Re: sphinx-build is really slow, any way to improve that?

[Markus Armbruster <armbru@redhat.com>]

Peter Maydell <peter.maydell@linaro.org> writes:

> On Mon, 5 Sept 2022 at 20:51, Claudio Fontana <cfontana@suse.de> wrote:
>> when I build qemu, there is a lot of time spent at the end of the build where one cpu goes 100% on sphinx-build.
>>
>> Is there some way to parallelize that? It seems it is the current bottleneck for rebuilds for me..
>
> It's a big fat python program, so I suspect not, but
> maybe I'm wrong.
>
> You can always configure --disable-docs if you don't care
> about the docs and want to make builds faster.

I care about the docs, but the impact on turnaround time is so bad I
stopped building the docs in the build trees I use for development, and
instead keep a separate tree that has docs enabled.  Tends to delay
diagnosis of doc markup errors, but that's the lesser evil for me.

We used to have a similar problem with generated C: touch the QAPI
schema, rebuild everything and its dog.  That was because everything and
its dog depended on the generated QAPI header.  C projects 101: putting
everything in a single header slows down rebuilds.

We solved this by splitting up the generated header, and updating
generated headers only when they actually change.

I have no idea whether Sphinx could do a similarly incremental rebuild.