[PATCH] ath79/ag71xx: rearrange ag71xx structs to remove holes

[Adrian Schmutzler]

> -----Original Message-----
> From: openwrt-devel [mailto:openwrt-devel-bounces at lists.openwrt.org]
> On Behalf Of Rui Salvaterra
> Sent: Sonntag, 19. September 2021 12:39
> To: openwrt-devel at lists.openwrt.org
> Cc: rosenp at gmail.com; Rui Salvaterra <rsalvaterra at gmail.com>
> Subject: [PATCH] ath79/ag71xx: rearrange ag71xx structs to remove holes

Commit title prefix should be "ath79: ag71xx:" or just "ath79:".

Apart from that, I can contribute nothing useful :-(

Best

Adrian

> 
> From: Rosen Penev <rosenp at gmail.com>
> 
> Remove ____cacheline_aligned attribute to ring structs. This actually
causes
> holes in the ag71xx struct as well as lower performance.
> 
> Rearrange struct members to fall within respective cachelines. The RX ring
> struct now does not share a cacheline with the TX ring. The NAPI struct
now
> takes up its own cachelines and does not share.
> 
> According to pahole -C ag71xx -c 32
> 
> Before:
> 
> struct ag71xx {
> 	/* size: 384, cachelines: 12, members: 22 */
> 	/* sum members: 375, holes: 2, sum holes: 9 */
> 
> After:
> 
> struct ag71xx {
> 	/* size: 376, cachelines: 12, members: 22 */
> 	/* last cacheline: 24 bytes */
> 
> Signed-off-by: Rosen Penev <rosenp at gmail.com> [Fix typos in the patch
> description]
> Signed-off-by: Rui Salvaterra <rsalvaterra at gmail.com>
> ---
> The ag71xx_ring changes are already part of the upstream driver. However,
> since we're not using it at all yet, let's apply this to our driver for
the time
> being, as David explicitly requests performance numbers before applying it
> upstream [1] (and rightly so, in my opinion).
> 
> [1]
> https://lore.kernel.org/netdev/20190725.112108.2287417619951369896.dave
> m at davemloft.net/
> 
>  .../net/ethernet/atheros/ag71xx/ag71xx.h      | 32 ++++++++++---------
>  1 file changed, 17 insertions(+), 15 deletions(-)
> 
> diff --git
> a/target/linux/ath79/files/drivers/net/ethernet/atheros/ag71xx/ag71xx.h
> b/target/linux/ath79/files/drivers/net/ethernet/atheros/ag71xx/ag71xx.h
> index 5ff9439f0d..6ed1f78459 100644
> ---
> a/target/linux/ath79/files/drivers/net/ethernet/atheros/ag71xx/ag71xx.h
> +++ b/target/linux/ath79/files/drivers/net/ethernet/atheros/ag71xx/ag71x
> +++ x.h
> @@ -107,13 +107,16 @@ struct ag71xx_buf {  };
> 
>  struct ag71xx_ring {
> -	struct ag71xx_buf	*buf;
> -	u8			*descs_cpu;
> -	dma_addr_t		descs_dma;
> -	u16			desc_split;
> -	u16			order;
> +	/* "Hot" fields in the data path. */
>  	unsigned int		curr;
>  	unsigned int		dirty;
> +
> +	/* "Cold" fields - not used in the data path. */
> +	struct ag71xx_buf	*buf;
> +	u16			order;
> +	u16			desc_split;
> +	dma_addr_t		descs_dma;
> +	u8			*descs_cpu;
>  };
> 
>  struct ag71xx_int_stats {
> @@ -151,21 +154,20 @@ struct ag71xx {
>  	 * Critical data related to the per-packet data path are clustered
>  	 * early in this structure to help improve the D-cache footprint.
>  	 */
> -	struct ag71xx_ring	rx_ring ____cacheline_aligned;
> -	struct ag71xx_ring	tx_ring ____cacheline_aligned;
> +	struct ag71xx_ring	rx_ring;
> +	u16			rx_buf_size;
> +	u16			rx_buf_offset;
> +	u32			msg_enable;
> 
> +	struct ag71xx_ring	tx_ring;
>  	int			mac_idx;
> -
>  	u16			desc_pktlen_mask;
> -	u16			rx_buf_size;
> -	u8			rx_buf_offset;
>  	u8			tx_hang_workaround:1;
> 
> +	struct napi_struct	napi;
>  	struct net_device	*dev;
>  	struct platform_device  *pdev;
>  	spinlock_t		lock;
> -	struct napi_struct	napi;
> -	u32			msg_enable;
> 
>  	/*
>  	 * From this point onwards we're not looking at per-packet fields.
> @@ -188,12 +190,12 @@ struct ag71xx {
>  	unsigned int		speed;
>  	int			duplex;
> 
> -	struct delayed_work	restart_work;
> -	struct timer_list	oom_timer;
> -
>  	struct reset_control *mac_reset;
>  	struct reset_control *mdio_reset;
> 
> +	struct delayed_work	restart_work;
> +	struct timer_list	oom_timer;
> +
>  	u32			fifodata[3];
>  	u32			plldata[3];
>  	u32			pllreg[3];
> --
> 2.33.0
> 
> 
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