From ea211225754ba3fc1c2afb290bf26bd714125b24 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?R=C3=A9mi=20Verschelde?= Date: Sun, 17 Jul 2022 01:09:18 +0200 Subject: SCons: Default `num_jobs` to max CPUs minus 1 if not specified This doesn't change the behavior when `--jobs`/`-j` is specified as a command-line argument or in `SCONSFLAGS`. The SCons hack used to know if `num_jobs` was set by the user is derived from the MongoDB setup. We use `os.cpu_count()` for portability (available since Python 3.4). With 4 CPUs or less, we use the max. With more than 4 we use max - 1 to preserve some bandwidth for the user's other programs. --- SConstruct | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) (limited to 'SConstruct') diff --git a/SConstruct b/SConstruct index 50cb43b218..0eba93e4ff 100644 --- a/SConstruct +++ b/SConstruct @@ -399,6 +399,24 @@ if selected_platform in platform_list: env = env_base.Clone() + # Default num_jobs to local cpu count if not user specified. + # SCons has a peculiarity where user-specified options won't be overridden + # by SetOption, so we can rely on this to know if we should use our default. + initial_num_jobs = env.GetOption("num_jobs") + altered_num_jobs = initial_num_jobs + 1 + env.SetOption("num_jobs", altered_num_jobs) + if env.GetOption("num_jobs") == altered_num_jobs: + cpu_count = os.cpu_count() + if cpu_count is None: + print("Couldn't auto-detect CPU count to configure build parallelism. Specify it with the -j argument.") + else: + safer_cpu_count = cpu_count if cpu_count <= 4 else cpu_count - 1 + print( + "Auto-detected %d CPU cores available for build parallelism. Using %d cores by default. You can override it with the -j argument." + % (cpu_count, safer_cpu_count) + ) + env.SetOption("num_jobs", safer_cpu_count) + if env["compiledb"]: # Generating the compilation DB (`compile_commands.json`) requires SCons 4.0.0 or later. from SCons import __version__ as scons_raw_version -- cgit v1.2.3