tracing: Uninline trace_trigger_soft_disabled() partly
authorChristophe Leroy <christophe.leroy@csgroup.eu>
Fri, 11 Feb 2022 07:10:18 +0000 (08:10 +0100)
committerSteven Rostedt (Google) <rostedt@goodmis.org>
Fri, 25 Feb 2022 17:07:01 +0000 (12:07 -0500)
commitbc82c38a6933aab308387d4aca47e0a05de7b553
tree3e3b025d70d013e4530f70f22861d736bd804bee
parentb61edd57740de5895f44f2ea417b164d9e1708bb
tracing: Uninline trace_trigger_soft_disabled() partly

On a powerpc32 build with CONFIG_CC_OPTIMISE_FOR_SIZE, the inline
keyword is not honored and trace_trigger_soft_disabled() appears
approx 50 times in vmlinux.

Adding -Winline to the build, the following message appears:

./include/linux/trace_events.h:712:1: error: inlining failed in call to 'trace_trigger_soft_disabled': call is unlikely and code size would grow [-Werror=inline]

That function is rather big for an inlined function:

c003df60 <trace_trigger_soft_disabled>:
c003df60: 94 21 ff f0  stwu    r1,-16(r1)
c003df64: 7c 08 02 a6  mflr    r0
c003df68: 90 01 00 14  stw     r0,20(r1)
c003df6c: bf c1 00 08  stmw    r30,8(r1)
c003df70: 83 e3 00 24  lwz     r31,36(r3)
c003df74: 73 e9 01 00  andi.   r9,r31,256
c003df78: 41 82 00 10  beq     c003df88 <trace_trigger_soft_disabled+0x28>
c003df7c: 38 60 00 00  li      r3,0
c003df80: 39 61 00 10  addi    r11,r1,16
c003df84: 4b fd 60 ac  b       c0014030 <_rest32gpr_30_x>
c003df88: 73 e9 00 80  andi.   r9,r31,128
c003df8c: 7c 7e 1b 78  mr      r30,r3
c003df90: 41 a2 00 14  beq     c003dfa4 <trace_trigger_soft_disabled+0x44>
c003df94: 38 c0 00 00  li      r6,0
c003df98: 38 a0 00 00  li      r5,0
c003df9c: 38 80 00 00  li      r4,0
c003dfa0: 48 05 c5 f1  bl      c009a590 <event_triggers_call>
c003dfa4: 73 e9 00 40  andi.   r9,r31,64
c003dfa8: 40 82 00 28  bne     c003dfd0 <trace_trigger_soft_disabled+0x70>
c003dfac: 73 ff 02 00  andi.   r31,r31,512
c003dfb0: 41 82 ff cc  beq     c003df7c <trace_trigger_soft_disabled+0x1c>
c003dfb4: 80 01 00 14  lwz     r0,20(r1)
c003dfb8: 83 e1 00 0c  lwz     r31,12(r1)
c003dfbc: 7f c3 f3 78  mr      r3,r30
c003dfc0: 83 c1 00 08  lwz     r30,8(r1)
c003dfc4: 7c 08 03 a6  mtlr    r0
c003dfc8: 38 21 00 10  addi    r1,r1,16
c003dfcc: 48 05 6f 6c  b       c0094f38 <trace_event_ignore_this_pid>
c003dfd0: 38 60 00 01  li      r3,1
c003dfd4: 4b ff ff ac  b       c003df80 <trace_trigger_soft_disabled+0x20>

However it is located in a hot path so inlining it is important.
But forcing inlining of the entire function by using __always_inline
leads to increasing the text size by approx 20 kbytes.

Instead, split the fonction in two parts, one part with the likely
fast path, flagged __always_inline, and a second part out of line.

With this change, on a powerpc32 with CONFIG_CC_OPTIMISE_FOR_SIZE
vmlinux text increases by only 1,4 kbytes, which is partly
compensated by a decrease of vmlinux data by 7 kbytes.

On ppc64_defconfig which has CONFIG_CC_OPTIMISE_FOR_SPEED, this
change reduces vmlinux text by more than 30 kbytes.

Link: https://lkml.kernel.org/r/69ce0986a52d026d381d612801d978aa4f977460.1644563295.git.christophe.leroy@csgroup.eu
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
include/linux/trace_events.h
kernel/trace/trace_events_trigger.c