Re: [PATCH 2/2] doc: Add section about ccache usage

[Jan Kiszka <jan.kiszka@siemens.com>]

On 13.09.21 17:10, Uladzimir Bely wrote:
> Signed-off-by: Uladzimir Bely <ubely@ilbers.de>
> ---
>  doc/user_manual.md | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/doc/user_manual.md b/doc/user_manual.md
> index 1da0e9d..903f9ae 100644
> --- a/doc/user_manual.md
> +++ b/doc/user_manual.md
> @@ -18,6 +18,7 @@ Copyright (C) 2016-2019, ilbers GmbH
>   - [Add a New Image Type](#add-a-new-image-type)
>   - [Add a Custom Application](#add-a-custom-application)
>   - [Enabling Cross-compilation](#isar-cross-compilation)
> + - [Using ccache for custom packages](#using-ccache-for-custom-packages)
>   - [Create an ISAR SDK root filesystem](#create-an-isar-sdk-root-filesystem)
>   - [Create a containerized Isar SDK root filesystem](#create-a-containerized-isar-sdk-root-filesystem)
>   - [Creation of local apt repo caching upstream Debian packages](#creation-of-local-apt-repo-caching-upstream-debian-packages)
> @@ -896,6 +897,21 @@ package build. To invoke it, just call
>  `bitbake mc:${MACHINE}-${DISTRO}:<package_name> -c devshell`.
>  
>  
> +## Using ccache for custom packages
> +
> +While base system is created from binary debian repositories, some user
> +packages are built from sources. It's possible to reduce build time
> +for such packages by enabling ccache.
> +
> +To enable global ccache functionality, `INHERIT += ccache` can be added
> +to `local.conf`. If some package requires ccache to be always disabled,
> +`CCACHE_DISABLE = '1'` can be used in the recipe.

Why so complex? ISAR_CROSS_COMPILE is managed with a single variable,
including per-recipe out-out/in. Would be better to follow that pattern
consistently.

> +
> +By default, ccache directory is created inside `TMPDIR`, but it can be
> +adjusted by `CCACHE_TOP_DIR` variable in `local.conf`. Ccache directory
> +`CCACHE_DIR` default value is `"${CCACHE_TOP_DIR}/${DISTRO}-${MACHINE}"`,

DISTRO-DISTRO_ARCH, just like for other cachings. There is nothing
machine-specific in the cache.

Jan

> +that means caches for different distros and machines are not overlapped.
> +
>  ## Create an ISAR SDK root filesystem
>  
>  ### Motivation
> 

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