kbuild: use -flive-patching when CONFIG_LIVEPATCH is enabled
GCC 9 introduces a new option, -flive-patching. It disables certain
optimizations which could make a compilation unsafe for later live
patching of the running kernel.
The option is used only if CONFIG_LIVEPATCH is enabled and $(CC)
supports it.
Performance impact of the option was measured on three different
Intel machines - two bigger NUMA boxes and one smaller UMA box. Kernel
intensive (IO, scheduling, networking) benchmarks were selected, plus a
set of HPC workloads from NAS Parallel Benchmark. The tests were done on
upstream kernel 5.0-rc8 with openSUSE Leap 15.0 userspace.
The majority of the tests is unaffected. The only significant exception
is the scheduler section which suffers 1-3% degradation.
Evaluated-by: Giovanni Gherdovich <ggherdovich@suse.cz>
Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
diff --git a/Makefile b/Makefile
index 60a4732..f8d8000 100644
--- a/Makefile
+++ b/Makefile
@@ -796,6 +796,10 @@
LDFLAGS_vmlinux += --gc-sections
endif
+ifdef CONFIG_LIVEPATCH
+KBUILD_CFLAGS += $(call cc-option, -flive-patching=inline-clone)
+endif
+
# arch Makefile may override CC so keep this after arch Makefile is included
NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include)