Immediate values provide a way to use dynamic code patching to update variables sitting within the instruction stream. It saves caches lines normally used by static read mostly variables. Enable it by default, but let users disable it through the EMBEDDED menu with the "Disable immediate values" submenu entry. Note: Since I think that I really should let embedded systems developers using RO memory the option to disable the immediate values, I choose to leave this menu option there, in the EMBEDDED menu. Also, the "CONFIG_IMMEDIATE" makes sense because we want to compile out all the immediate code when we decide not to use optimized immediate values at all (it removes otherwise unused code). Signed-off-by: Mathieu Desnoyers CC: Adrian Bunk CC: Andi Kleen CC: Alexey Dobriyan CC: Christoph Hellwig --- init/Kconfig | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) Index: linux-2.6-lttng/init/Kconfig =================================================================== --- linux-2.6-lttng.orig/init/Kconfig 2007-11-13 13:33:54.000000000 -0500 +++ linux-2.6-lttng/init/Kconfig 2007-11-13 13:50:02.000000000 -0500 @@ -423,6 +423,17 @@ config CC_OPTIMIZE_FOR_SIZE config SYSCTL bool +config IMMEDIATE + default y if !DISABLE_IMMEDIATE + depends on ARCH_SUPPORTS_IMMEDIATE + bool + help + Immediate values are used as read-mostly variables that are rarely + updated. They use code patching to modify the values inscribed in the + instruction stream. It provides a way to save precious cache lines + that would otherwise have to be used by these variables. They can be + disabled through the EMBEDDED menu. + menuconfig EMBEDDED bool "Configure standard kernel features (for small systems)" help @@ -658,6 +669,16 @@ config MARKERS source "arch/Kconfig" +config DISABLE_IMMEDIATE + default y if EMBEDDED + bool "Disable immediate values" if EMBEDDED + depends on ARCH_SUPPORTS_IMMEDIATE + help + Disable code patching based immediate values for embedded systems. It + consumes slightly more memory and requires to modify the instruction + stream each time a variable is updated. Should really be disabled for + embedded systems with read-only text. + endmenu # General setup config RT_MUTEXES -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/