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Subject[PATCH 0/4] jump label patches

hi,

For background, I introduced this patchset in:
http://marc.info/?l=linux-kernel&m=125200966226921&w=2

This patchset updates the jump label mechanism to look like:

#define JUMP_LABEL(tag, label, cond) \
do { \
static const char __jlstrtab_##tag[] \
__used __attribute__((section("__jump_strings"))) = #tag; \
asm goto ("1:" \
"jmp %l[" #label "] \n\t" \
".pushsection __jump_table, \"a\" \n\t" \
_ASM_PTR "1b, %l[" #label "], %c0, 0 \n\t" \
".popsection \n\t" \
: : "i" (__jlstrtab_##tag) : : label); \
} while (0)
#endif


and usage case is:

#define DECLARE_TRACE(name, proto, args) \
extern struct tracepoint __tracepoint_##name; \
static inline void trace_##name(proto) \
{ \
JUMP_LABEL(name, trace_label, __tracepoint_##name.state);\
__DO_TRACE(&__tracepoint_##name, \
TP_PROTO(proto), TP_ARGS(args)); \
trace_label: \
return; \
} \

So the idea now, is that by default we jump over the disabled code. In order to
enable the 'disabled' code, or tracing, we simply replace the jump with a
'jump 0'. Thus, we now avoid the issue of not having enough instruction space.
Thus, in most cases the jump we are patching is an '0xeb' opcode which is
simply 2 bytes (occasionally its an 0xeb). I have this patchset working nicely
on x86_64. I'm not sure if we need to recognize additional jump opcodes for
x86 32-bit....I have not yet tested there. In my x86_64 testing under memory
pressure I saw about a 30 cycle improvement with this code per tracepoint.
Additionally, this code reduces the icache bytes from 9 bytes (cmpl; je), to
just 2 bytes (jmp).
The patchset makes use of text_poke_fixup() interface introduced by Masami in:
http://marc.info/?l=linux-kernel&m=125297186224609&w=2.

Thus, that patchset needs to be applied first. Patch is against the latest -tip
tree.

thanks,

-Jason



arch/x86/include/asm/jump_label.h | 27 +++++++++++
arch/x86/kernel/Makefile | 2 +-
arch/x86/kernel/jump_label.c | 94 +++++++++++++++++++++++++++++++++++++
include/asm-generic/vmlinux.lds.h | 11 ++++
include/linux/jump_label.h | 71 ++++++++++++++++++++++++++++
include/linux/kernel.h | 1 +
include/linux/module.h | 12 ++++-
include/linux/tracepoint.h | 31 +++++++------
kernel/extable.c | 2 +-
kernel/module.c | 31 ++++++++++++
kernel/tracepoint.c | 10 ++++
11 files changed, 275 insertions(+), 17 deletions(-)
create mode 100644 arch/x86/include/asm/jump_label.h
create mode 100644 arch/x86/kernel/jump_label.c
create mode 100644 include/linux/jump_label.h


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