diff options
Diffstat (limited to 'arch/Kconfig')
| -rw-r--r-- | arch/Kconfig | 41 |
1 files changed, 33 insertions, 8 deletions
diff --git a/arch/Kconfig b/arch/Kconfig index 2505740b81d2..5b448a74d0f7 100644 --- 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. + 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 i386, options added to the compiler flags may increase - the size of the kernel slightly. + ( 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 @@ -185,4 +196,18 @@ config HAVE_RCU_TABLE_FREE config ARCH_HAVE_NMI_SAFE_CMPXCHG bool +config HAVE_ALIGNED_STRUCT_PAGE + bool + help + This makes sure that struct pages are double word aligned and that + e.g. the SLUB allocator can perform double word atomic operations + on a struct page for better performance. However selecting this + might increase the size of a struct page by a word. + +config HAVE_CMPXCHG_LOCAL + bool + +config HAVE_CMPXCHG_DOUBLE + bool + source "kernel/gcov/Kconfig" |