From b235848f40ed3ca8fabbac6273aa085cee467ef1 Mon Sep 17 00:00:00 2001 From: Linus Torvalds <torvalds@linux-foundation.org> Date: Tue, 18 Jun 2024 09:00:04 -0700 Subject: [PATCH] cpumask: limit FORCE_NR_CPUS to just the UP case [ Upstream commit 5d272dd1b3430bb31fa30042490fa081512424e4 ] Hardcoding the number of CPUs at compile time does improve code generation, but if you get it wrong the result will be confusion. We already limited this earlier to only "experts" (see commit fe5759d5bfda "cpumask: limit visibility of FORCE_NR_CPUS"), but with distro kernel configs often having EXPERT enabled, that turns out to not be much of a limit. To quote the philosophers at Disney: "Everyone can be an expert. And when everyone's an expert, no one will be". There's a runtime warning if you then set nr_cpus to anything but the forced number, but apparently that can be ignored too [1] and by then it's pretty much too late anyway. If we had some real way to limit this to "embedded only", maybe it would be worth it, but let's see if anybody even notices that the option is gone. We need to simplify kernel configuration anyway. Link: https://lore.kernel.org/all/20240618105036.208a8860@rorschach.local.home/ [1] Reported-by: Steven Rostedt <rostedt@goodmis.org> Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Paul McKenney <paulmck@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Yury Norov <yury.norov@gmail.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org> --- lib/Kconfig | 8 +------- 1 file changed, 1 insertion(+), 7 deletions(-) diff --git a/lib/Kconfig b/lib/Kconfig index c686f4adc124..ee365b7402f1 100644 --- a/lib/Kconfig +++ b/lib/Kconfig @@ -539,13 +539,7 @@ config CPUMASK_OFFSTACK stack overflow. config FORCE_NR_CPUS - bool "Set number of CPUs at compile time" - depends on SMP && EXPERT && !COMPILE_TEST - help - Say Yes if you have NR_CPUS set to an actual number of possible - CPUs in your system, not to a default value. This forces the core - code to rely on compile-time value and optimize kernel routines - better. + def_bool !SMP config CPU_RMAP bool