linux-kernel - Re: [PATCH] tracing: uninline trace_trigger_soft

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Date:   Thu, 10 Feb 2022 09:26:17 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH] tracing: uninline trace_trigger_soft_disabled()

On Thu, 10 Feb 2022 09:47:52 +0100
Christophe Leroy <christophe.leroy@...roup.eu> wrote:

> On a ppc32 build with CONFIG_CC_OPTIMISE_FOR_SIZE,
> trace_trigger_soft_disabled() appears more than 50 times in vmlinux.
> 
> That function is rather big for an inlined function, and
> it doesn't benefit much from inlining as its only parameter
> is a pointer to a struct in memory:

The number of parameters is not the reason for it being inlined. It's in a
*very* hot path, and a function call causes a noticeable performance hit.


> 
> 	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>
> 
> It doesn't benefit much from inlining as its only parameter is a
> pointer to a struct in memory so no constant folding is involved.
> 
> Uninline it and move it into kernel/trace/trace_events_trigger.c
> 
> It reduces the size of vmlinux by approximately 10 kbytes.

If you have an issue with the size, perhaps the function can be modified to
condense it. I'm happy to have a size reduction, but I will NACK making it
into a function call.

-- Steve