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Date: Wed, 29 May 2024 23:52:30 +0300
From: Sergey Shtylyov <s.shtylyov@....ru>
To: Paul Barker <paul.barker.ct@...renesas.com>, "David S. Miller"
<davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
<kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
Niklas Söderlund <niklas.soderlund+renesas@...natech.se>
CC: Biju Das <biju.das.jz@...renesas.com>, Claudiu Beznea
<claudiu.beznea.uj@...renesas.com>, Yoshihiro Shimoda
<yoshihiro.shimoda.uh@...esas.com>, <netdev@...r.kernel.org>,
<linux-renesas-soc@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [net-next PATCH v4 7/7] net: ravb: Allocate RX buffers via page
pool
On 5/28/24 6:03 PM, Paul Barker wrote:
> This patch makes multiple changes that can't be separated:
>
> 1) Allocate plain RX buffers via a page pool instead of allocating
> SKBs, then use build_skb() when a packet is received.
> 2) For GbEth IP, reduce the RX buffer size to 2kB.
> 3) For GbEth IP, merge packets which span more than one RX descriptor
> as SKB fragments instead of copying data.
>
> Implementing (1) without (2) would require the use of an order-1 page
> pool (instead of an order-0 page pool split into page fragments) for
> GbEth.
>
> Implementing (2) without (3) would leave us no space to re-assemble
> packets which span more than one RX descriptor.
>
> Implementing (3) without (1) would not be possible as the network stack
> expects to use put_page() or page_pool_put_page() to free SKB fragments
> after an SKB is consumed.
>
> RX checksum offload support is adjusted to handle both linear and
> nonlinear (fragmented) packets.
>
> This patch gives the following improvements during testing with iperf3.
>
> * RZ/G2L:
> * TCP RX: same bandwidth at -43% CPU load (70% -> 40%)
> * UDP RX: same bandwidth at -17% CPU load (88% -> 74%)
>
> * RZ/G2UL:
> * TCP RX: +30% bandwidth (726Mbps -> 941Mbps)
> * UDP RX: +417% bandwidth (108Mbps -> 558Mbps)
>
> * RZ/G3S:
> * TCP RX: +64% bandwidth (562Mbps -> 920Mbps)
> * UDP RX: +420% bandwidth (90Mbps -> 468Mbps)
>
> * RZ/Five:
> * TCP RX: +217% bandwidth (145Mbps -> 459Mbps)
> * UDP RX: +470% bandwidth (20Mbps -> 114Mbps)
>
> There is no significant impact on bandwidth or CPU load in testing on
> RZ/G2H or R-Car M3N.
>
> Signed-off-by: Paul Barker <paul.barker.ct@...renesas.com>
> ---
> Changes v3->v4:
> * Used a separate page pool for each RX queue.
> * Passed struct ravb_rx_desc to ravb_alloc_rx_buffer() so that we can
> simplify the calling function.
> * Explained the calculation of rx_desc->ds_cc.
> * Added handling of nonlinear SKBs in ravb_rx_csum_gbeth().
>
> drivers/net/ethernet/renesas/ravb.h | 10 +-
> drivers/net/ethernet/renesas/ravb_main.c | 230 ++++++++++++++---------
> 2 files changed, 146 insertions(+), 94 deletions(-)
>
> diff --git a/drivers/net/ethernet/renesas/ravb.h b/drivers/net/ethernet/renesas/ravb.h
> index 6a7aa7dd17e6..f2091a17fcf7 100644
> --- a/drivers/net/ethernet/renesas/ravb.h
> +++ b/drivers/net/ethernet/renesas/ravb.h
[...]> @@ -1094,7 +1099,8 @@ struct ravb_private {
> struct ravb_tx_desc *tx_ring[NUM_TX_QUEUE];
> void *tx_align[NUM_TX_QUEUE];
> struct sk_buff *rx_1st_skb;
> - struct sk_buff **rx_skb[NUM_RX_QUEUE];
> + struct page_pool *rx_pool[NUM_RX_QUEUE];
Don't we need #include <net/page_pool/types.h>
[...]
> diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
> index dd92f074881a..bb7f7d44be6e 100644
> --- a/drivers/net/ethernet/renesas/ravb_main.c
> +++ b/drivers/net/ethernet/renesas/ravb_main.c
[...]
> @@ -317,35 +289,56 @@ static void ravb_ring_free(struct net_device *ndev, int q)
> priv->tx_skb[q] = NULL;
> }
>
> +static int
> +ravb_alloc_rx_buffer(struct net_device *ndev, int q, u32 entry, gfp_t gfp_mask,
> + struct ravb_rx_desc *rx_desc)
> +{
> + struct ravb_private *priv = netdev_priv(ndev);
> + const struct ravb_hw_info *info = priv->info;
> + struct ravb_rx_buffer *rx_buff = &priv->rx_buffers[q][entry];
> + dma_addr_t dma_addr;
> + unsigned int size;
> +
> + size = info->rx_buffer_size;
> + rx_buff->page = page_pool_alloc(priv->rx_pool[q], &rx_buff->offset, &size,
> + gfp_mask);
> + if (unlikely(!rx_buff->page)) {
> + /* We just set the data size to 0 for a failed mapping
> + * which should prevent DMA from happening...
> + */
> + rx_desc->ds_cc = cpu_to_le16(0);
> + return -ENOMEM;
> + }
> +
> + dma_addr = page_pool_get_dma_addr(rx_buff->page) + rx_buff->offset;
> + dma_sync_single_for_device(ndev->dev.parent, dma_addr,
> + info->rx_buffer_size, DMA_FROM_DEVICE);
Do we really need this call?
> + rx_desc->dptr = cpu_to_le32(dma_addr);
> +
> + /* The end of the RX buffer is used to store skb shared data, so we need
> + * to ensure that the hardware leaves enough space for this.
> + */
> + rx_desc->ds_cc = cpu_to_le16(info->rx_buffer_size
> + - SKB_DATA_ALIGN(sizeof(struct skb_shared_info))
Please leave the - operator on the previous line...
> + - ETH_FCS_LEN + sizeof(__sum16));
Here as well...
> + return 0;
> +}
> +
> static u32
> ravb_rx_ring_refill(struct net_device *ndev, int q, u32 count, gfp_t gfp_mask)
> {
> struct ravb_private *priv = netdev_priv(ndev);
> - const struct ravb_hw_info *info = priv->info;
> struct ravb_rx_desc *rx_desc;
> - dma_addr_t dma_addr;
> u32 i, entry;
>
> for (i = 0; i < count; i++) {
> entry = (priv->dirty_rx[q] + i) % priv->num_rx_ring[q];
> rx_desc = ravb_rx_get_desc(priv, q, entry);
> - rx_desc->ds_cc = cpu_to_le16(info->rx_max_desc_use);
>
> - if (!priv->rx_skb[q][entry]) {
> - priv->rx_skb[q][entry] = ravb_alloc_skb(ndev, info, gfp_mask);
> - if (!priv->rx_skb[q][entry])
> + if (!priv->rx_buffers[q][entry].page) {
> + if (unlikely(ravb_alloc_rx_buffer(ndev, q, entry,
Well, IIRC Greg KH is against using unlikely() unless you have actually
instrumented the code and this gives an improvement... have you? :-)
[...]
> @@ -727,12 +739,22 @@ static void ravb_rx_csum_gbeth(struct sk_buff *skb)
> if (unlikely(skb->len < sizeof(__sum16) * 2))
> return;
>
> - hw_csum = skb_tail_pointer(skb) - sizeof(__sum16);
> + if (skb_is_nonlinear(skb)) {
> + last_frag = &shinfo->frags[shinfo->nr_frags - 1];
> + hw_csum = skb_frag_address(last_frag) + skb_frag_size(last_frag) - sizeof(__sum16);
> + } else {
> + hw_csum = skb_tail_pointer(skb) - sizeof(__sum16);
> + }
We can do the subtraction only once here...
[...]
> @@ -816,14 +824,26 @@ static int ravb_rx_gbeth(struct net_device *ndev, int budget, int q)
> if (desc_status & MSC_CEEF)
> stats->rx_missed_errors++;
> } else {
> + struct ravb_rx_buffer *rx_buff = &priv->rx_buffers[q][entry];
> + void *rx_addr = page_address(rx_buff->page) + rx_buff->offset;
Need an empty line here...
> die_dt = desc->die_dt & 0xF0;
> - skb = ravb_get_skb_gbeth(ndev, entry, desc);
> + dma_sync_single_for_cpu(ndev->dev.parent, le32_to_cpu(desc->dptr),
> + desc_len, DMA_FROM_DEVICE);
> +
> switch (die_dt) {
> case DT_FSINGLE:
> case DT_FSTART:
> /* Start of packet:
> - * Set initial data length.
> + * Prepare an SKB and add initial data.
I'd prefer calling it skb in the comments...
[...]
> @@ -865,7 +894,16 @@ static int ravb_rx_gbeth(struct net_device *ndev, int budget, int q)
> stats->rx_bytes += skb->len;
> napi_gro_receive(&priv->napi[q], skb);
> rx_packets++;
> +
> + /* Clear rx_1st_skb so that it will only be
> + * non-NULL when valid.
> + */
> + if (die_dt == DT_FEND)
> + priv->rx_1st_skb = NULL;
Hm, can't we do this under *case* DT_FEND above?
[...]
MBR, Sergey
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