c5905afb0e
So here's a boot tested patch on top of Jason's series that does
all the cleanups I talked about and turns jump labels into a
more intuitive to use facility. It should also address the
various misconceptions and confusions that surround jump labels.
Typical usage scenarios:
#include <linux/static_key.h>
struct static_key key = STATIC_KEY_INIT_TRUE;
if (static_key_false(&key))
do unlikely code
else
do likely code
Or:
if (static_key_true(&key))
do likely code
else
do unlikely code
The static key is modified via:
static_key_slow_inc(&key);
...
static_key_slow_dec(&key);
The 'slow' prefix makes it abundantly clear that this is an
expensive operation.
I've updated all in-kernel code to use this everywhere. Note
that I (intentionally) have not pushed through the rename
blindly through to the lowest levels: the actual jump-label
patching arch facility should be named like that, so we want to
decouple jump labels from the static-key facility a bit.
On non-jump-label enabled architectures static keys default to
likely()/unlikely() branches.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Jason Baron <jbaron@redhat.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: a.p.zijlstra@chello.nl
Cc: mathieu.desnoyers@efficios.com
Cc: davem@davemloft.net
Cc: ddaney.cavm@gmail.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20120222085809.GA26397@elte.hu
Signed-off-by: Ingo Molnar <mingo@elte.hu>
213 lines
5.9 KiB
Text
213 lines
5.9 KiB
Text
#
|
|
# General architecture dependent options
|
|
#
|
|
|
|
config OPROFILE
|
|
tristate "OProfile system profiling"
|
|
depends on PROFILING
|
|
depends on HAVE_OPROFILE
|
|
select RING_BUFFER
|
|
select RING_BUFFER_ALLOW_SWAP
|
|
help
|
|
OProfile is a profiling system capable of profiling the
|
|
whole system, include the kernel, kernel modules, libraries,
|
|
and applications.
|
|
|
|
If unsure, say N.
|
|
|
|
config OPROFILE_EVENT_MULTIPLEX
|
|
bool "OProfile multiplexing support (EXPERIMENTAL)"
|
|
default n
|
|
depends on OPROFILE && X86
|
|
help
|
|
The number of hardware counters is limited. The multiplexing
|
|
feature enables OProfile to gather more events than counters
|
|
are provided by the hardware. This is realized by switching
|
|
between events at an user specified time interval.
|
|
|
|
If unsure, say N.
|
|
|
|
config HAVE_OPROFILE
|
|
bool
|
|
|
|
config OPROFILE_NMI_TIMER
|
|
def_bool y
|
|
depends on PERF_EVENTS && HAVE_PERF_EVENTS_NMI
|
|
|
|
config KPROBES
|
|
bool "Kprobes"
|
|
depends on MODULES
|
|
depends on HAVE_KPROBES
|
|
select KALLSYMS
|
|
help
|
|
Kprobes allows you to trap at almost any kernel address and
|
|
execute a callback function. register_kprobe() establishes
|
|
a probepoint and specifies the callback. Kprobes is useful
|
|
for kernel debugging, non-intrusive instrumentation and testing.
|
|
If in doubt, say "N".
|
|
|
|
config JUMP_LABEL
|
|
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 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
|
|
depends on KPROBES && HAVE_OPTPROBES
|
|
depends on !PREEMPT
|
|
|
|
config HAVE_EFFICIENT_UNALIGNED_ACCESS
|
|
bool
|
|
help
|
|
Some architectures are unable to perform unaligned accesses
|
|
without the use of get_unaligned/put_unaligned. Others are
|
|
unable to perform such accesses efficiently (e.g. trap on
|
|
unaligned access and require fixing it up in the exception
|
|
handler.)
|
|
|
|
This symbol should be selected by an architecture if it can
|
|
perform unaligned accesses efficiently to allow different
|
|
code paths to be selected for these cases. Some network
|
|
drivers, for example, could opt to not fix up alignment
|
|
problems with received packets if doing so would not help
|
|
much.
|
|
|
|
See Documentation/unaligned-memory-access.txt for more
|
|
information on the topic of unaligned memory accesses.
|
|
|
|
config HAVE_SYSCALL_WRAPPERS
|
|
bool
|
|
|
|
config KRETPROBES
|
|
def_bool y
|
|
depends on KPROBES && HAVE_KRETPROBES
|
|
|
|
config USER_RETURN_NOTIFIER
|
|
bool
|
|
depends on HAVE_USER_RETURN_NOTIFIER
|
|
help
|
|
Provide a kernel-internal notification when a cpu is about to
|
|
switch to user mode.
|
|
|
|
config HAVE_IOREMAP_PROT
|
|
bool
|
|
|
|
config HAVE_KPROBES
|
|
bool
|
|
|
|
config HAVE_KRETPROBES
|
|
bool
|
|
|
|
config HAVE_OPTPROBES
|
|
bool
|
|
#
|
|
# An arch should select this if it provides all these things:
|
|
#
|
|
# task_pt_regs() in asm/processor.h or asm/ptrace.h
|
|
# arch_has_single_step() if there is hardware single-step support
|
|
# arch_has_block_step() if there is hardware block-step support
|
|
# asm/syscall.h supplying asm-generic/syscall.h interface
|
|
# linux/regset.h user_regset interfaces
|
|
# CORE_DUMP_USE_REGSET #define'd in linux/elf.h
|
|
# TIF_SYSCALL_TRACE calls tracehook_report_syscall_{entry,exit}
|
|
# TIF_NOTIFY_RESUME calls tracehook_notify_resume()
|
|
# signal delivery calls tracehook_signal_handler()
|
|
#
|
|
config HAVE_ARCH_TRACEHOOK
|
|
bool
|
|
|
|
config HAVE_DMA_ATTRS
|
|
bool
|
|
|
|
config USE_GENERIC_SMP_HELPERS
|
|
bool
|
|
|
|
config HAVE_REGS_AND_STACK_ACCESS_API
|
|
bool
|
|
help
|
|
This symbol should be selected by an architecure if it supports
|
|
the API needed to access registers and stack entries from pt_regs,
|
|
declared in asm/ptrace.h
|
|
For example the kprobes-based event tracer needs this API.
|
|
|
|
config HAVE_CLK
|
|
bool
|
|
help
|
|
The <linux/clk.h> calls support software clock gating and
|
|
thus are a key power management tool on many systems.
|
|
|
|
config HAVE_DMA_API_DEBUG
|
|
bool
|
|
|
|
config HAVE_HW_BREAKPOINT
|
|
bool
|
|
depends on PERF_EVENTS
|
|
|
|
config HAVE_MIXED_BREAKPOINTS_REGS
|
|
bool
|
|
depends on HAVE_HW_BREAKPOINT
|
|
help
|
|
Depending on the arch implementation of hardware breakpoints,
|
|
some of them have separate registers for data and instruction
|
|
breakpoints addresses, others have mixed registers to store
|
|
them but define the access type in a control register.
|
|
Select this option if your arch implements breakpoints under the
|
|
latter fashion.
|
|
|
|
config HAVE_USER_RETURN_NOTIFIER
|
|
bool
|
|
|
|
config HAVE_PERF_EVENTS_NMI
|
|
bool
|
|
help
|
|
System hardware can generate an NMI using the perf event
|
|
subsystem. Also has support for calculating CPU cycle events
|
|
to determine how many clock cycles in a given period.
|
|
|
|
config HAVE_ARCH_JUMP_LABEL
|
|
bool
|
|
|
|
config HAVE_ARCH_MUTEX_CPU_RELAX
|
|
bool
|
|
|
|
config HAVE_RCU_TABLE_FREE
|
|
bool
|
|
|
|
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"
|