Re: [PATCH v2 01/12] gitlab: enable ccache for many build jobs

["Daniel P. Berrangé" <berrange@redhat.com>]

On Fri, Aug 25, 2023 at 10:46:29AM +0300, Michael Tokarev wrote:
> 24.08.2023 19:38, Alex Bennée wrote:
> > From: Daniel P. Berrangé <berrange@redhat.com>
> > 
> > The `ccache` tool can be very effective at reducing compilation times
> > when re-running pipelines with only minor changes each time. For example
> > a fresh 'build-system-fedora' job will typically take 20 minutes on the
> > gitlab.com shared runners. With ccache this is reduced to as little as
> > 6 minutes.
> 
> I've been using ccache when building qemu in debian, for quite a while.
> 
> The problem here, in the way qemu build system works, is that the cache
> is hugely dependent on the path to the source. You change just one char
> in there (/build/qemu/v8.1.0/ => /build/qemu/v8.1.1) and whole cache becomes
> unusable, it all gets compiled anew.  This is because qemu build sys uses
> absolute file names when building, and this is detected by ccache, so
> the source dir gets mixed into the hash together with gcc version and
> other things.
> 
> Dunno how well this will work in the qemu ci though.

Should be fine, as gitlab always checks out code in a fixed directory
name matching the git repo name.

With regards,
Daniel
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