jump labels/x86: Use etiher 5 byte or 2 byte jumps
Have the jump labels add a "jmp" in the assembly instead
of a default nop. This will cause the assembler to put in
either a 2 byte or 5 byte jmp depending on where the target
lable is.
Then at compile time, the update_jump_label code will replace
the jmps with either 2 or 5 byte nops.
On boot up, the code can be examined to see if the jump label
uses either a 2 or 5 byte nop and replace it.
By allowing the jump labels to be 2 bytes, it speeds up the
nops, not only 2 byte nops are faster than 5 byte nops, but also
because it saves on cache foot print.
text data bss dec hex filename
13403667 3666856 2998272 20068795 13239bb ../nobackup/mxtest/vmlinux-old
13398536 3666856 2998272 20063664 13225b0 ../nobackup/mxtest/vmlinux-new
Converting the current v3.2 trace points saved 5,131 bytes.
As more places use jump labels, this will have a bigger savings.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
3 files changed
