Merge tag 'nfs-for-3.4-1' of git://git.linux-nfs.org/projects/trondmy/linux-nfs

[karo-tx-linux.git] / arch / Kconfig

diff --git a/arch/Kconfig b/arch/Kconfig
index 4f55c736be11ea3aa3ac6762b0ec3d1371b872ce..5b448a74d0f756a41eb275639efef22186f55d66 100644 (file)
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -47,18 +47,29 @@ config KPROBES
          If in doubt, say "N".
 
 config JUMP_LABEL
-       bool "Optimize trace point call sites"
+       bool "Optimize very unlikely/likely branches"
        depends on HAVE_ARCH_JUMP_LABEL
        help
+         This option enables a transparent branch optimization that
+        makes certain almost-always-true or almost-always-false branch
+        conditions even cheaper to execute within the kernel.
+
+        Certain performance-sensitive kernel code, such as trace points,
+        scheduler functionality, networking code and KVM have such
+        branches and include support for this optimization technique.
+
          If it is detected that the compiler has support for "asm goto",
-        the kernel will compile trace point locations with just a
-        nop instruction. When trace points are enabled, the nop will
-        be converted to a jump to the trace function. This technique
-        lowers overhead and stress on the branch prediction of the
-        processor.
-
-        On i386, options added to the compiler flags may increase
-        the size of the kernel slightly.
+        the kernel will compile such branches with just a nop
+        instruction. When the condition flag is toggled to true, the
+        nop will be converted to a jump instruction to execute the
+        conditional block of instructions.
+
+        This technique lowers overhead and stress on the branch prediction
+        of the processor and generally makes the kernel faster. The update
+        of the condition is slower, but those are always very rare.
+
+        ( On 32-bit x86, the necessary options added to the compiler
+          flags may increase the size of the kernel slightly. )
 
 config OPTPROBES
        def_bool y