Subject: Re: [PATCH net-next] net: ethernet: ti: cpsw: replace unnecessarily macroses on functions

From: Ivan Khoronzhuk <[email-masked]>
Date: Fri, 27 Jul 2018 23:23:49 +0300

On Fri, Jul 27, 2018 at 01:04:22PM -0700, Joe Perches wrote:
>On Fri, 2018-07-27 at 22:36 +0300, Ivan Khoronzhuk wrote:
>> On Fri, Jul 27, 2018 at 12:21:07PM -0700, Joe Perches wrote:
>> > On Fri, 2018-07-27 at 22:13 +0300, Ivan Khoronzhuk wrote:
>> > > Replace ugly macroses on functions.
>> >
>> > Careful, see below.
>> >
>> > > diff --git a/drivers/net/ethernet/ti/cpsw.c b/drivers/net/ethernet/ti/cpsw.c
>> >
>> > []
>> > > @@ -565,40 +565,40 @@ static const struct cpsw_stats cpsw_gstrings_ch_stats[] = {
>> > >  				(func)(slave++, ##arg);			\
>> > >  	} while (0)
>> > >
>> > > -#define cpsw_dual_emac_src_port_detect(cpsw, status, ndev, skb)		\
>> > > -	do {								\
>> > > -		if (!cpsw->data.dual_emac)				\
>> > > -			break;						\
>> > > -		if (CPDMA_RX_SOURCE_PORT(status) == 1) {		\
>> > > -			ndev = cpsw->slaves[0].ndev;			\
>> > > -			skb->dev = ndev;				\
>> > > -		} else if (CPDMA_RX_SOURCE_PORT(status) == 2) {		\
>> > > -			ndev = cpsw->slaves[1].ndev;			\
>> > > -			skb->dev = ndev;				\
>> > > -		}							\
>> > > -	} while (0)
>> > > -#define cpsw_add_mcast(cpsw, priv, addr)				\
>> > > -	do {								\
>> > > -		if (cpsw->data.dual_emac) {				\
>> > > -			struct cpsw_slave *slave = cpsw->slaves +	\
>> > > -						priv->emac_port;	\
>> > > -			int slave_port = cpsw_get_slave_port(		\
>> > > -						slave->slave_num);	\
>> > > -			cpsw_ale_add_mcast(cpsw->ale, addr,		\
>> > > -				1 << slave_port | ALE_PORT_HOST,	\
>> > > -				ALE_VLAN, slave->port_vlan, 0);		\
>> > > -		} else {						\
>> > > -			cpsw_ale_add_mcast(cpsw->ale, addr,		\
>> > > -				ALE_ALL_PORTS,				\
>> > > -				0, 0, 0);				\
>> > > -		}							\
>> > > -	} while (0)
>> > > -
>> > >  static inline int cpsw_get_slave_port(u32 slave_num)
>> > >  {
>> > >  	return slave_num + 1;
>> > >  }
>> > >
>> > > +static inline void cpsw_src_port_detect(struct cpsw_common *cpsw, int status,
>> > > +					struct sk_buff *skb)
>> > > +{
>> > > +	if (!cpsw->data.dual_emac)
>> > > +		return;
>> > > +
>> > > +	if (CPDMA_RX_SOURCE_PORT(status) == 1)
>> > > +		skb->dev = cpsw->slaves[0].ndev;
>> > > +	else if (CPDMA_RX_SOURCE_PORT(status) == 2)
>> > > +		skb->dev = cpsw->slaves[1].ndev;
>> > > +}
>> >
>> > perhaps better as a switch/case
>>
>> not better, it's shorter.
>
>True for the source code but it compiles to more object code.
>
>$ cat foo.c
>struct cpsw_common {
>	struct {
>		int dual_emac;
>	} data;
>	struct {
>		int ndev;
>	} slaves[2];
>};
>
>struct sk_buff {
>	int dev;
>};
>
>#define CPDMA_RX_SOURCE_PORT(__status__)        ((__status__ >> 16) & 0x7)
>
>#if defined SWITCH
>
>void foo(struct cpsw_common *cpsw, int status, struct sk_buff *skb)
>{
>	if (!cpsw->data.dual_emac)
>		return;
>
>	switch (CPDMA_RX_SOURCE_PORT(status)) {
>	case 1:
>		skb->dev = cpsw->slaves[0].ndev;
>		break;
>	case 2:
>		skb->dev = cpsw->slaves[1].ndev;
>		break;
>	}
>}
>
>#else
>
>void foo(struct cpsw_common *cpsw, int status, struct sk_buff *skb)
>{
>	if (!cpsw->data.dual_emac)
>		return;
>
>	if (CPDMA_RX_SOURCE_PORT(status) == 1)
>		skb->dev = cpsw->slaves[0].ndev;
>	else if (CPDMA_RX_SOURCE_PORT(status) == 2)
>		skb->dev = cpsw->slaves[1].ndev;
>}
>
>#endif
>$ gcc -c -O2 -DSWITCH foo.c
>$ size foo.o
>   text	   data	    bss	    dec	    hex	filename
>     94	      0	      0	     94	     5e	foo.o
>$ objdump -d foo.o
>
>foo.o:     file format elf64-x86-64
>
>
>Disassembly of section .text:
>
>0000000000000000 <foo>:
>   0:	8b 07                	mov    (%rdi),%eax
>   2:	85 c0                	test   %eax,%eax
>   4:	74 15                	je     1b <foo+0x1b>
>   6:	c1 fe 10             	sar    $0x10,%esi
>   9:	83 e6 07             	and    $0x7,%esi
>   c:	83 fe 01             	cmp    $0x1,%esi
>   f:	74 17                	je     28 <foo+0x28>
>  11:	83 fe 02             	cmp    $0x2,%esi
>  14:	75 0a                	jne    20 <foo+0x20>
>  16:	8b 47 08             	mov    0x8(%rdi),%eax
>  19:	89 02                	mov    %eax,(%rdx)
>  1b:	f3 c3                	repz retq
>  1d:	0f 1f 00             	nopl   (%rax)
>  20:	f3 c3                	repz retq
>  22:	66 0f 1f 44 00 00    	nopw   0x0(%rax,%rax,1)
>  28:	8b 47 04             	mov    0x4(%rdi),%eax
>  2b:	89 02                	mov    %eax,(%rdx)
>  2d:	c3                   	retq
>$ gcc -c -O2 foo.c
>$ size foo.o
>   text	   data	    bss	    dec	    hex	filename
>    102	      0	      0	    102	     66	foo.o
>$ objdump -d foo.o
>
>foo.o:     file format elf64-x86-64
>
>
>Disassembly of section .text:
>
>0000000000000000 <foo>:
>   0:	8b 07                	mov    (%rdi),%eax
>   2:	85 c0                	test   %eax,%eax
>   4:	74 10                	je     16 <foo+0x16>
>   6:	c1 fe 10             	sar    $0x10,%esi
>   9:	83 e6 07             	and    $0x7,%esi
>   c:	83 fe 01             	cmp    $0x1,%esi
>   f:	74 0f                	je     20 <foo+0x20>
>  11:	83 fe 02             	cmp    $0x2,%esi
>  14:	74 1a                	je     30 <foo+0x30>
>  16:	f3 c3                	repz retq
>  18:	0f 1f 84 00 00 00 00 	nopl   0x0(%rax,%rax,1)
>  1f:	00
>  20:	8b 47 04             	mov    0x4(%rdi),%eax
>  23:	89 02                	mov    %eax,(%rdx)
>  25:	c3                   	retq
>  26:	66 2e 0f 1f 84 00 00 	nopw   %cs:0x0(%rax,%rax,1)
>  2d:	00 00 00
>  30:	8b 47 08             	mov    0x8(%rdi),%eax
>  33:	89 02                	mov    %eax,(%rdx)
>  35:	c3                   	retq
>
>

This driver, mainly used for ARM

For ARM, situation a little bit different:
$ arm-linux-gnueabihf-gcc -c -O2 -DSWITCH foo.c
$ size foo.o
   text	   data	    bss	    dec	    hex	filename
     32	      0	      0	     32	     20	foo.o

$ arm-linux-gnueabihf-objdump -d foo.o

foo.o:     file format elf32-littlearm

Disassembly of section .text:

00000000 <foo>:
   0:	6803      	ldr	r3, [r0, #0]
   2:	b143      	cbz	r3, 16 <foo+0x16>
   4:	f3c1 4102 	ubfx	r1, r1, #16, #3
   8:	2901      	cmp	r1, #1
   a:	d005      	beq.n	18 <foo+0x18>
   c:	2902      	cmp	r1, #2
   e:	d000      	beq.n	12 <foo+0x12>
  10:	4770      	bx	lr
  12:	6883      	ldr	r3, [r0, #8]
  14:	6013      	str	r3, [r2, #0]
  16:	4770      	bx	lr
  18:	6843      	ldr	r3, [r0, #4]
  1a:	6013      	str	r3, [r2, #0]
  1c:	4770      	bx	lr
  1e:	bf00      	nop

$ arm-linux-gnueabihf-gcc -c -O2 foo.c
$ size foo.o
   text	   data	    bss	    dec	    hex	filename
     28	      0	      0	     28	     1c	foo.o

$ arm-linux-gnueabihf-objdump -d foo.o

foo.o:     file format elf32-littlearm

Disassembly of section .text:

00000000 <foo>:
   0:	6803      	ldr	r3, [r0, #0]
   2:	b13b      	cbz	r3, 14 <foo+0x14>
   4:	f3c1 4102 	ubfx	r1, r1, #16, #3
   8:	2901      	cmp	r1, #1
   a:	d004      	beq.n	16 <foo+0x16>
   c:	2902      	cmp	r1, #2
   e:	bf04      	itt	eq
  10:	6883      	ldreq	r3, [r0, #8]
  12:	6013      	streq	r3, [r2, #0]
  14:	4770      	bx	lr
  16:	6843      	ldr	r3, [r0, #4]
  18:	6013      	str	r3, [r2, #0]
  1a:	4770      	bx	lr

So, it's shorter.

-- 
Regards,
Ivan Khoronzhuk