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Message-ID: <BLU0-SMTP122B5D616AD665A29B9DDEFAC090@phx.gbl>
Date: Mon, 28 Oct 2013 23:50:19 -0700
From: Nathan Hintz <nlhintz@...mail.com>
To: OpenWrt Development List <openwrt-devel@...ts.openwrt.org>
CC: zajec5@...il.com, netdev@...r.kernel.org,
"David S. Miller" <davem@...emloft.net>
Subject: Re: [OpenWrt-Devel] [RFC TRY#2][PATCH] bgmac: pass received packet
to the netif instead of copying it
On Mon, 28 Oct 2013 18:42:22 +0100
Rafał Miłecki <zajec5@...il.com> wrote:
Hi:
A few questions/comments inline...
Nathan
> Copying whole packets with skb_copy_from_linear_data_offset is a pretty
> bad idea. CPU was spending time in __copy_user_common and network
> performance was lower. With the new solution iperf-measured speed
> increased from 116Mb/s to 134Mb/s.
>
> Another way to improve performance could be switching to build_skb. It
> is cache-specific, so will require testing of various devices.
>
> Signed-off-by: Rafał Miłecki <zajec5@...il.com>
> ---
> drivers/net/ethernet/broadcom/bgmac.c | 71 ++++++++++++++++++++-------------
> 1 file changed, 44 insertions(+), 27 deletions(-)
>
> diff --git a/drivers/net/ethernet/broadcom/bgmac.c b/drivers/net/ethernet/broadcom/bgmac.c
> index 6b7541f..fde9a11 100644
> --- a/drivers/net/ethernet/broadcom/bgmac.c
> +++ b/drivers/net/ethernet/broadcom/bgmac.c
> @@ -307,7 +307,6 @@ static int bgmac_dma_rx_read(struct bgmac *bgmac, struct bgmac_dma_ring *ring,
> struct device *dma_dev = bgmac->core->dma_dev;
> struct bgmac_slot_info *slot = &ring->slots[ring->start];
> struct sk_buff *skb = slot->skb;
> - struct sk_buff *new_skb;
> struct bgmac_rx_header *rx;
> u16 len, flags;
>
> @@ -320,38 +319,56 @@ static int bgmac_dma_rx_read(struct bgmac *bgmac, struct bgmac_dma_ring *ring,
> len = le16_to_cpu(rx->len);
> flags = le16_to_cpu(rx->flags);
>
> - /* Check for poison and drop or pass the packet */
> - if (len == 0xdead && flags == 0xbeef) {
> - bgmac_err(bgmac, "Found poisoned packet at slot %d, DMA issue!\n",
> - ring->start);
> - } else {
> + do {
"old_skb" duplicates "skb" stored above, can that one be used (renamed) instead of creating a new one here?
> + struct sk_buff *old_skb = slot->skb;
> + dma_addr_t old_dma_addr = slot->dma_addr;
> + int err;
> +
> + /* Check for poison and drop or pass the packet */
> + if (len == 0xdead && flags == 0xbeef) {
> + bgmac_err(bgmac, "Found poisoned packet at slot %d, DMA issue!\n",
> + ring->start);
Nothing in the buffer has been changed by the cpu yet, so is this sync necessary?
> + dma_sync_single_for_device(dma_dev,
> + slot->dma_addr,
> + BGMAC_RX_BUF_SIZE,
> + DMA_FROM_DEVICE);
> + break;
> + }
> +
> /* Omit CRC. */
> len -= ETH_FCS_LEN;
>
> - new_skb = netdev_alloc_skb_ip_align(bgmac->net_dev, len);
> - if (new_skb) {
> - skb_put(new_skb, len);
> - skb_copy_from_linear_data_offset(skb, BGMAC_RX_FRAME_OFFSET,
> - new_skb->data,
> - len);
> - skb_checksum_none_assert(skb);
> - new_skb->protocol =
> - eth_type_trans(new_skb, bgmac->net_dev);
> - netif_receive_skb(new_skb);
> - handled++;
> - } else {
> - bgmac->net_dev->stats.rx_dropped++;
> - bgmac_err(bgmac, "Allocation of skb for copying packet failed!\n");
> + /* Prepare new skb as replacement */
> + err = bgmac_dma_rx_skb_for_slot(bgmac, slot);
> + if (err) {
I've sent a separate patch against "bgmac_dma_rx_skb_for_slot" to not corrupt the slot at all if an
error occurs (skb alloc or dma mapping), and free the skb that was allocated if a dma mapping error
occurs. Assuming that patch is accepted, then the following two lines would not be needed.
With "bgmac_dma_rx_skb_for_slot" as it currently exists, this would leak an skb for a dma mapping
error (this was pre-existing to the changes in this patch).
> + slot->skb = old_skb;
> + slot->dma_addr = old_dma_addr;
> +
> + /* Poison the old skb */
> + rx->len = cpu_to_le16(0xdead);
> + rx->flags = cpu_to_le16(0xbeef);
> +
> + dma_sync_single_for_device(dma_dev,
> + slot->dma_addr,
> + BGMAC_RX_BUF_SIZE,
> + DMA_FROM_DEVICE);
> + break;
> }
> + bgmac_dma_rx_setup_desc(bgmac, ring, ring->start);
>
> - /* Poison the old skb */
> - rx->len = cpu_to_le16(0xdead);
> - rx->flags = cpu_to_le16(0xbeef);
> - }
> + /* Unmap old skb, we'll pass it to the netfif */
> + dma_unmap_single(dma_dev, old_dma_addr,
> + BGMAC_RX_BUF_SIZE,
> + DMA_FROM_DEVICE);
> +
> + skb_put(skb, BGMAC_RX_FRAME_OFFSET + len);
> + skb_pull(skb, BGMAC_RX_FRAME_OFFSET);
>
> - /* Make it back accessible to the hardware */
> - dma_sync_single_for_device(dma_dev, slot->dma_addr,
> - BGMAC_RX_BUF_SIZE, DMA_FROM_DEVICE);
> + skb_checksum_none_assert(skb);
> + skb->protocol = eth_type_trans(skb, bgmac->net_dev);
> + netif_receive_skb(skb);
> + handled++;
> + } while (0);
>
> if (++ring->start >= BGMAC_RX_RING_SLOTS)
> ring->start = 0;
--
Nathan
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