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

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 24/8/23 18:38, 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.
> 
> Normally meson would auto-detect existance of ccache in $PATH and use
> it automatically, but the way we wrap meson from configure breaks this,
> as we're passing in an config file with explicitly set compiler paths.
> Thus we need to add $CCACHE_WRAPPERSPATH to the front of $PATH. For
> unknown reasons if doing this in msys though, gcc becomes unable to
> invoke 'cc1' when run from meson. For msys we thus set CC='ccache gcc'
> before invoking 'configure' instead.
> 
> A second problem with msys is that cache misses are incredibly
> expensive, so enabling ccache massively slows down the build when
> the cache isn't well populated. This is suspected to be a result of
> the cost of spawning processes under the msys architecture. To deal
> with this we set CCACHE_DEPEND=1 which enables ccache's 'depend_only'
> strategy. This avoids extra spawning of the pre-processor during
> cache misses, with the downside that is it less likely ccache will
> find a cache hit after semantically benign compiler flag changes.
> This is the lesser of two evils, as otherwise we can't use ccache
> at all under msys and remain inside the job time limit.
> 
> If people are finding ccache to hurt their pipelines, it can be
> disabled by setting the 'CCACHE_DISABLE=1' env variable against
> their gitlab fork CI settings.
> 
> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> Message-Id: <20230804111054.281802-2-berrange@redhat.com>
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> ---
>   docs/devel/ci-jobs.rst.inc                    |  7 +++++
>   .gitlab-ci.d/buildtest-template.yml           | 11 ++++++++
>   .gitlab-ci.d/crossbuild-template.yml          | 26 +++++++++++++++++++
>   .gitlab-ci.d/windows.yml                      | 13 ++++++++--
>   .../dockerfiles/debian-hexagon-cross.docker   |  9 ++++++-
>   5 files changed, 63 insertions(+), 3 deletions(-)

Very nice, thanks!

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>