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

[Joe Perches]

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