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Date: Mon, 19 Aug 2019 16:55:22 -0700
From: Jakub Kicinski <jakub.kicinski@...ronome.com>
To: Thomas Bogendoerfer <tbogendoerfer@...e.de>
Cc: Jonathan Corbet <corbet@....net>,
Ralf Baechle <ralf@...ux-mips.org>,
Paul Burton <paul.burton@...s.com>,
James Hogan <jhogan@...nel.org>,
Dmitry Torokhov <dmitry.torokhov@...il.com>,
Lee Jones <lee.jones@...aro.org>,
"David S. Miller" <davem@...emloft.net>,
Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
Alessandro Zummo <a.zummo@...ertech.it>,
Alexandre Belloni <alexandre.belloni@...tlin.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Jiri Slaby <jslaby@...e.com>,
Evgeniy Polyakov <zbr@...emap.net>, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org,
linux-input@...r.kernel.org, netdev@...r.kernel.org,
linux-rtc@...r.kernel.org, linux-serial@...r.kernel.org
Subject: Re: [PATCH v5 10/17] net: sgi: ioc3-eth: rework skb rx handling
On Mon, 19 Aug 2019 18:31:33 +0200, Thomas Bogendoerfer wrote:
> Buffers alloacted by alloc_skb() are already cache aligned so there
> is no need for an extra align done by ioc3_alloc_skb. And instead
> of skb_put/skb_trim simply use one skb_put after frame size is known
> during receive.
>
> Signed-off-by: Thomas Bogendoerfer <tbogendoerfer@...e.de>
> ---
> drivers/net/ethernet/sgi/ioc3-eth.c | 50 ++++++++-----------------------------
> 1 file changed, 11 insertions(+), 39 deletions(-)
>
> diff --git a/drivers/net/ethernet/sgi/ioc3-eth.c b/drivers/net/ethernet/sgi/ioc3-eth.c
> index c875640926d6..d862f28887f9 100644
> --- a/drivers/net/ethernet/sgi/ioc3-eth.c
> +++ b/drivers/net/ethernet/sgi/ioc3-eth.c
> @@ -11,7 +11,6 @@
> *
> * To do:
> *
> - * o Handle allocation failures in ioc3_alloc_skb() more gracefully.
> * o Handle allocation failures in ioc3_init_rings().
> * o Use prefetching for large packets. What is a good lower limit for
> * prefetching?
> @@ -72,6 +71,12 @@
> #define TX_RING_ENTRIES 128
> #define TX_RING_MASK (TX_RING_ENTRIES - 1)
>
> +/* BEWARE: The IOC3 documentation documents the size of rx buffers as
> + * 1644 while it's actually 1664. This one was nasty to track down...
> + */
> +#define RX_OFFSET 10
> +#define RX_BUF_SIZE 1664
> +
> #define ETCSR_FD ((17 << ETCSR_IPGR2_SHIFT) | (11 << ETCSR_IPGR1_SHIFT) | 21)
> #define ETCSR_HD ((21 << ETCSR_IPGR2_SHIFT) | (21 << ETCSR_IPGR1_SHIFT) | 21)
>
> @@ -111,31 +116,6 @@ static void ioc3_init(struct net_device *dev);
> static const char ioc3_str[] = "IOC3 Ethernet";
> static const struct ethtool_ops ioc3_ethtool_ops;
>
> -/* We use this to acquire receive skb's that we can DMA directly into. */
> -
> -#define IOC3_CACHELINE 128UL
Is the cache line on the platform this driver works on 128B?
This looks like a DMA engine alignment requirement, more than an
optimization.
The comment in __alloc_skb() says:
/* We do our best to align skb_shared_info on a separate cache
* line. It usually works because kmalloc(X > SMP_CACHE_BYTES) gives
* aligned memory blocks, unless SLUB/SLAB debug is enabled.
* Both skb->head and skb_shared_info are cache line aligned.
*/
note the "unless".
> -static inline unsigned long aligned_rx_skb_addr(unsigned long addr)
> -{
> - return (~addr + 1) & (IOC3_CACHELINE - 1UL);
> -}
> -
> -static inline struct sk_buff *ioc3_alloc_skb(unsigned long length,
> - unsigned int gfp_mask)
> -{
> - struct sk_buff *skb;
> -
> - skb = alloc_skb(length + IOC3_CACHELINE - 1, gfp_mask);
> - if (likely(skb)) {
> - int offset = aligned_rx_skb_addr((unsigned long)skb->data);
> -
> - if (offset)
> - skb_reserve(skb, offset);
> - }
> -
> - return skb;
> -}
> -
> static inline unsigned long ioc3_map(void *ptr, unsigned long vdev)
> {
> #ifdef CONFIG_SGI_IP27
> @@ -148,12 +128,6 @@ static inline unsigned long ioc3_map(void *ptr, unsigned long vdev)
> #endif
> }
>
> -/* BEWARE: The IOC3 documentation documents the size of rx buffers as
> - * 1644 while it's actually 1664. This one was nasty to track down ...
> - */
> -#define RX_OFFSET 10
> -#define RX_BUF_ALLOC_SIZE (1664 + RX_OFFSET + IOC3_CACHELINE)
> -
> #define IOC3_SIZE 0x100000
>
> static inline u32 mcr_pack(u32 pulse, u32 sample)
> @@ -534,10 +508,10 @@ static inline void ioc3_rx(struct net_device *dev)
> err = be32_to_cpu(rxb->err); /* It's valid ... */
> if (err & ERXBUF_GOODPKT) {
> len = ((w0 >> ERXBUF_BYTECNT_SHIFT) & 0x7ff) - 4;
> - skb_trim(skb, len);
> + skb_put(skb, len);
> skb->protocol = eth_type_trans(skb, dev);
>
> - new_skb = ioc3_alloc_skb(RX_BUF_ALLOC_SIZE, GFP_ATOMIC);
> + new_skb = alloc_skb(RX_BUF_SIZE, GFP_ATOMIC);
> if (!new_skb) {
> /* Ouch, drop packet and just recycle packet
> * to keep the ring filled.
> @@ -546,6 +520,7 @@ static inline void ioc3_rx(struct net_device *dev)
> new_skb = skb;
> goto next;
> }
> + new_skb->dev = dev;
Assigning dev pointer seems unrelated to the rest of the patch?
> if (likely(dev->features & NETIF_F_RXCSUM))
> ioc3_tcpudp_checksum(skb,
> @@ -556,8 +531,6 @@ static inline void ioc3_rx(struct net_device *dev)
>
> ip->rx_skbs[rx_entry] = NULL; /* Poison */
>
> - /* Because we reserve afterwards. */
> - skb_put(new_skb, (1664 + RX_OFFSET));
> rxb = (struct ioc3_erxbuf *)new_skb->data;
> skb_reserve(new_skb, RX_OFFSET);
>
> @@ -846,16 +819,15 @@ static void ioc3_alloc_rings(struct net_device *dev)
> for (i = 0; i < RX_BUFFS; i++) {
> struct sk_buff *skb;
>
> - skb = ioc3_alloc_skb(RX_BUF_ALLOC_SIZE, GFP_ATOMIC);
> + skb = alloc_skb(RX_BUF_SIZE, GFP_ATOMIC);
> if (!skb) {
> show_free_areas(0, NULL);
> continue;
> }
> + skb->dev = dev;
>
> ip->rx_skbs[i] = skb;
>
> - /* Because we reserve afterwards. */
> - skb_put(skb, (1664 + RX_OFFSET));
> rxb = (struct ioc3_erxbuf *)skb->data;
> rxr[i] = cpu_to_be64(ioc3_map(rxb, 1));
> skb_reserve(skb, RX_OFFSET);
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