Re: [PATCH] net: introduce alloc_skb_order0

Eric Dumazet
2010-10-11T21:18:08Z

> 1) Allocation of a physically continous 16Kbytes bloc for the rx-ring,
> at device initialization (GFP_KERNEL OK here)
>
> Here, the only thing you could do is to not allocate real skbs but
> only 16KB data blocs (no need for the sk_buf, only the ->data part), and
> force copybreak for all incoming packets (remove the rx_copybreak
> tunable)
>

Here is the patch I cooked for net-next-2.6 to implement this idea.

I tested it on a dev machine and it works well.

[PATCH net-next] r8169: use 50% less ram for RX ring

Using standard skb allocations in r8169 leads to order-3 allocations (if
PAGE_SIZE=4096), because NIC needs 16383 bytes, and skb overhead makes
this bigger than 16384 -> 32768 bytes per "skb"

Using kmalloc() permits to reduce memory requirements of one r8169 nic
by 4Mbytes. (256 frames * 16Kbytes). This is fine since a hardware bug
requires us to copy incoming frames, so we build real skb when doing
this copy.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
---
drivers/net/r8169.c | 183 ++++++++++++++----------------------------
1 file changed, 64 insertions(+), 119 deletions(-)

diff --git a/drivers/net/r8169.c b/drivers/net/r8169.c
index bc669a4..1760533 100644
--- a/drivers/net/r8169.c
+++ b/drivers/net/r8169.c
@@ -187,12 +187,7 @@ static DEFINE_PCI_DEVICE_TABLE(rtl8169_pci_tbl) = {

MODULE_DEVICE_TABLE(pci, rtl8169_pci_tbl);

-/*
- * we set our copybreak very high so that we don't have
- * to allocate 16k frames all the time (see note in
- * rtl8169_open()
- */
-static int rx_copybreak = 16383;
+static int rx_buf_sz = 16383;
static int use_dac;
static struct {
u32 msg_enable;
@@ -484,10 +479,8 @@ struct rtl8169_private {
struct RxDesc *RxDescArray; /* 256-aligned Rx descriptor ring */
dma_addr_t TxPhyAddr;
dma_addr_t RxPhyAddr;
- struct sk_buff *Rx_skbuff[NUM_RX_DESC]; /* Rx data buffers */
+ void *Rx_databuff[NUM_RX_DESC]; /* Rx data buffers */
struct ring_info tx_skb[NUM_TX_DESC]; /* Tx data buffers */
- unsigned align;
- unsigned rx_buf_sz;
struct timer_list timer;
u16 cp_cmd;
u16 intr_event;
@@ -515,8 +508,6 @@ struct rtl8169_private {

MODULE_AUTHOR("Realtek and the Linux r8169 crew <netdev@vger.kernel.org>");
MODULE_DESCRIPTION("RealTek RTL-8169 Gigabit Ethernet driver");
-module_param(rx_copybreak, int, 0);
-MODULE_PARM_DESC(rx_copybreak, "Copy breakpoint for copy-only-tiny-frames");
module_param(use_dac, int, 0);
MODULE_PARM_DESC(use_dac, "Enable PCI DAC. Unsafe on 32 bit PCI slot.");
module_param_named(debug, debug.msg_enable, int, 0);
@@ -3196,7 +3187,6 @@ rtl8169_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
dev->features |= NETIF_F_GRO;

tp->intr_mask = 0xffff;
- tp->align = cfg->align;
tp->hw_start = cfg->hw_start;
tp->intr_event = cfg->intr_event;
tp->napi_event = cfg->napi_event;
@@ -3266,18 +3256,6 @@ static void __devexit rtl8169_remove_one(struct pci_dev *pdev)
pci_set_drvdata(pdev, NULL);
}

-static void rtl8169_set_rxbufsize(struct rtl8169_private *tp,
- unsigned int mtu)
-{
- unsigned int max_frame = mtu + VLAN_ETH_HLEN + ETH_FCS_LEN;
-
- if (max_frame != 16383)
- printk(KERN_WARNING PFX "WARNING! Changing of MTU on this "
- "NIC may lead to frame reception errors!\n");
-
- tp->rx_buf_sz = (max_frame > RX_BUF_SIZE) ? max_frame : RX_BUF_SIZE;
-}
-
static int rtl8169_open(struct net_device *dev)
{
struct rtl8169_private *tp = netdev_priv(dev);
@@ -3287,18 +3265,6 @@ static int rtl8169_open(struct net_device *dev)
pm_runtime_get_sync(&pdev->dev);

/*
- * Note that we use a magic value here, its wierd I know
- * its done because, some subset of rtl8169 hardware suffers from
- * a problem in which frames received that are longer than
- * the size set in RxMaxSize register return garbage sizes
- * when received. To avoid this we need to turn off filtering,
- * which is done by setting a value of 16383 in the RxMaxSize register
- * and allocating 16k frames to handle the largest possible rx value
- * thats what the magic math below does.
- */
- rtl8169_set_rxbufsize(tp, 16383 - VLAN_ETH_HLEN - ETH_FCS_LEN);
-
- /*
* Rx and Tx desscriptors needs 256 bytes alignment.
* dma_alloc_coherent provides more.
*/
@@ -3474,7 +3440,7 @@ static void rtl_hw_start_8169(struct net_device *dev)

RTL_W8(EarlyTxThres, EarlyTxThld);

- rtl_set_rx_max_size(ioaddr, tp->rx_buf_sz);
+ rtl_set_rx_max_size(ioaddr, rx_buf_sz);

if ((tp->mac_version == RTL_GIGA_MAC_VER_01) ||
(tp->mac_version == RTL_GIGA_MAC_VER_02) ||
@@ -3735,7 +3701,7 @@ static void rtl_hw_start_8168(struct net_device *dev)

RTL_W8(EarlyTxThres, EarlyTxThld);

- rtl_set_rx_max_size(ioaddr, tp->rx_buf_sz);
+ rtl_set_rx_max_size(ioaddr, rx_buf_sz);

tp->cp_cmd |= RTL_R16(CPlusCmd) | PktCntrDisable | INTT_1;

@@ -3915,7 +3881,7 @@ static void rtl_hw_start_8101(struct net_device *dev)

RTL_W8(EarlyTxThres, EarlyTxThld);

- rtl_set_rx_max_size(ioaddr, tp->rx_buf_sz);
+ rtl_set_rx_max_size(ioaddr, rx_buf_sz);

tp->cp_cmd |= rtl_rw_cpluscmd(ioaddr) | PCIMulRW;

@@ -3956,8 +3922,6 @@ static int rtl8169_change_mtu(struct net_device *dev, int new_mtu)

rtl8169_down(dev);

- rtl8169_set_rxbufsize(tp, dev->mtu);
-
ret = rtl8169_init_ring(dev);
if (ret < 0)
goto out;
@@ -3978,15 +3942,15 @@ static inline void rtl8169_make_unusable_by_asic(struct RxDesc *desc)
desc->opts1 &= ~cpu_to_le32(DescOwn | RsvdMask);
}

-static void rtl8169_free_rx_skb(struct rtl8169_private *tp,
- struct sk_buff **sk_buff, struct RxDesc *desc)
+static void rtl8169_free_rx_databuff(struct rtl8169_private *tp,
+ void **data_buff, struct RxDesc *desc)
{
struct pci_dev *pdev = tp->pci_dev;

- dma_unmap_single(&pdev->dev, le64_to_cpu(desc->addr), tp->rx_buf_sz,
+ dma_unmap_single(&pdev->dev, le64_to_cpu(desc->addr), rx_buf_sz,
PCI_DMA_FROMDEVICE);
- dev_kfree_skb(*sk_buff);
- *sk_buff = NULL;
+ kfree(*data_buff);
+ *data_buff = NULL;
rtl8169_make_unusable_by_asic(desc);
}

@@ -4005,33 +3969,34 @@ static inline void rtl8169_map_to_asic(struct RxDesc *desc, dma_addr_t mapping,
rtl8169_mark_to_asic(desc, rx_buf_sz);
}

-static struct sk_buff *rtl8169_alloc_rx_skb(struct pci_dev *pdev,
+static inline void *rtl8169_align(void *data)
+{
+ return (void *)ALIGN((long)data, 16);
+}
+
+static struct sk_buff *rtl8169_alloc_rx_data(struct pci_dev *pdev,
struct net_device *dev,
- struct RxDesc *desc, int rx_buf_sz,
- unsigned int align, gfp_t gfp)
+ struct RxDesc *desc)
{
- struct sk_buff *skb;
+ void *data;
dma_addr_t mapping;
- unsigned int pad;
+ int node = dev->dev.parent ? dev_to_node(dev->dev.parent) : -1;

- pad = align ? align : NET_IP_ALIGN;
+ data = kmalloc_node(rx_buf_sz, GFP_KERNEL, node);
+ if (!data)
+ return NULL;

- skb = __netdev_alloc_skb(dev, rx_buf_sz + pad, gfp);
- if (!skb)
- goto err_out;
-
- skb_reserve(skb, align ? ((pad - 1) & (unsigned long)skb->data) : pad);
-
- mapping = dma_map_single(&pdev->dev, skb->data, rx_buf_sz,
+ if (rtl8169_align(data) != data) {
+ kfree(data);
+ data = kmalloc_node(rx_buf_sz + 15, GFP_KERNEL, node);
+ if (!data)
+ return NULL;
+ }
+ mapping = dma_map_single(&pdev->dev, rtl8169_align(data), rx_buf_sz,
PCI_DMA_FROMDEVICE);

rtl8169_map_to_asic(desc, mapping, rx_buf_sz);
-out:
- return skb;
-
-err_out:
- rtl8169_make_unusable_by_asic(desc);
- goto out;
+ return data;
}

static void rtl8169_rx_clear(struct rtl8169_private *tp)
@@ -4039,8 +4004,8 @@ static void rtl8169_rx_clear(struct rtl8169_private *tp)
unsigned int i;

for (i = 0; i < NUM_RX_DESC; i++) {
- if (tp->Rx_skbuff[i]) {
- rtl8169_free_rx_skb(tp, tp->Rx_skbuff + i,
+ if (tp->Rx_databuff[i]) {
+ rtl8169_free_rx_databuff(tp, tp->Rx_databuff + i,
tp->RxDescArray + i);
}
}
@@ -4052,21 +4017,21 @@ static u32 rtl8169_rx_fill(struct rtl8169_private *tp, struct net_device *dev,
u32 cur;

for (cur = start; end - cur != 0; cur++) {
- struct sk_buff *skb;
+ void *data;
unsigned int i = cur % NUM_RX_DESC;

WARN_ON((s32)(end - cur) < 0);

- if (tp->Rx_skbuff[i])
+ if (tp->Rx_databuff[i])
continue;

- skb = rtl8169_alloc_rx_skb(tp->pci_dev, dev,
- tp->RxDescArray + i,
- tp->rx_buf_sz, tp->align, gfp);
- if (!skb)
+ data = rtl8169_alloc_rx_data(tp->pci_dev, dev,
+ tp->RxDescArray + i);
+ if (!data) {
+ rtl8169_make_unusable_by_asic(tp->RxDescArray + i);
break;
-
- tp->Rx_skbuff[i] = skb;
+ }
+ tp->Rx_databuff[i] = data;
}
return cur - start;
}
@@ -4088,7 +4053,7 @@ static int rtl8169_init_ring(struct net_device *dev)
rtl8169_init_ring_indexes(tp);

memset(tp->tx_skb, 0x0, NUM_TX_DESC * sizeof(struct ring_info));
- memset(tp->Rx_skbuff, 0x0, NUM_RX_DESC * sizeof(struct sk_buff *));
+ memset(tp->Rx_databuff, 0x0, NUM_RX_DESC * sizeof(void *));

if (rtl8169_rx_fill(tp, dev, 0, NUM_RX_DESC, GFP_KERNEL) != NUM_RX_DESC)
goto err_out;
@@ -4473,27 +4438,23 @@ static inline void rtl8169_rx_csum(struct sk_buff *skb, u32 opts1)
skb_checksum_none_assert(skb);
}

-static inline bool rtl8169_try_rx_copy(struct sk_buff **sk_buff,
- struct rtl8169_private *tp, int pkt_size,
- dma_addr_t addr)
+static struct sk_buff *rtl8169_try_rx_copy(void *data,
+ struct rtl8169_private *tp,
+ int pkt_size,
+ dma_addr_t addr)
{
struct sk_buff *skb;
- bool done = false;
-
- if (pkt_size >= rx_copybreak)
- goto out;
-
- skb = netdev_alloc_skb_ip_align(tp->dev, pkt_size);
- if (!skb)
- goto out;

+ data = rtl8169_align(data);
dma_sync_single_for_cpu(&tp->pci_dev->dev, addr, pkt_size,
PCI_DMA_FROMDEVICE);
- skb_copy_from_linear_data(*sk_buff, skb->data, pkt_size);
- *sk_buff = skb;
- done = true;
-out:
- return done;
+ prefetch(data);
+ skb = netdev_alloc_skb_ip_align(tp->dev, pkt_size);
+ if (skb)
+ memcpy(skb->data, data, pkt_size);
+ dma_sync_single_for_device(&tp->pci_dev->dev, addr, pkt_size,
+ PCI_DMA_FROMDEVICE);
+ return skb;
}

/*
@@ -4508,7 +4469,7 @@ static int rtl8169_rx_interrupt(struct net_device *dev,
void __iomem *ioaddr, u32 budget)
{
unsigned int cur_rx, rx_left;
- unsigned int delta, count;
+ unsigned int count;
int polling = (budget != ~(u32)0) ? 1 : 0;

cur_rx = tp->cur_rx;
@@ -4537,12 +4498,11 @@ static int rtl8169_rx_interrupt(struct net_device *dev,
rtl8169_schedule_work(dev, rtl8169_reset_task);
dev->stats.rx_fifo_errors++;
}
- rtl8169_mark_to_asic(desc, tp->rx_buf_sz);
+ rtl8169_mark_to_asic(desc, rx_buf_sz);
} else {
- struct sk_buff *skb = tp->Rx_skbuff[entry];
+ struct sk_buff *skb;
dma_addr_t addr = le64_to_cpu(desc->addr);
int pkt_size = (status & 0x00001FFF) - 4;
- struct pci_dev *pdev = tp->pci_dev;

/*
* The driver does not support incoming fragmented
@@ -4552,18 +4512,16 @@ static int rtl8169_rx_interrupt(struct net_device *dev,
if (unlikely(rtl8169_fragmented_frame(status))) {
dev->stats.rx_dropped++;
dev->stats.rx_length_errors++;
- rtl8169_mark_to_asic(desc, tp->rx_buf_sz);
+ rtl8169_mark_to_asic(desc, rx_buf_sz);
continue;
}

- if (rtl8169_try_rx_copy(&skb, tp, pkt_size, addr)) {
- dma_sync_single_for_device(&pdev->dev, addr,
- pkt_size, PCI_DMA_FROMDEVICE);
- rtl8169_mark_to_asic(desc, tp->rx_buf_sz);
- } else {
- dma_unmap_single(&pdev->dev, addr, tp->rx_buf_sz,
- PCI_DMA_FROMDEVICE);
- tp->Rx_skbuff[entry] = NULL;
+ skb = rtl8169_try_rx_copy(tp->Rx_databuff[entry],
+ tp, pkt_size, addr);
+ rtl8169_mark_to_asic(desc, rx_buf_sz);
+ if (!skb) {
+ dev->stats.rx_dropped++;
+ continue;
}

rtl8169_rx_csum(skb, status);
@@ -4592,20 +4550,7 @@ static int rtl8169_rx_interrupt(struct net_device *dev,
count = cur_rx - tp->cur_rx;
tp->cur_rx = cur_rx;

- delta = rtl8169_rx_fill(tp, dev, tp->dirty_rx, tp->cur_rx, GFP_ATOMIC);
- if (!delta && count)
- netif_info(tp, intr, dev, "no Rx buffer allocated\n");
- tp->dirty_rx += delta;
-
- /*
- * FIXME: until there is periodic timer to try and refill the ring,
- * a temporary shortage may definitely kill the Rx process.
- * - disable the asic to try and avoid an overflow and kick it again
- * after refill ?
- * - how do others driver handle this condition (Uh oh...).
- */
- if (tp->dirty_rx + NUM_RX_DESC == tp->cur_rx)
- netif_emerg(tp, intr, dev, "Rx buffers exhausted\n");
+ tp->dirty_rx += count;

return count;
}