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Date: Mon, 28 Jan 2019 13:18:55 +0100
From: Simon Horman <horms@...ge.net.au>
To: Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
Cc: netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
linux-renesas-soc@...r.kernel.org, linux-sh@...r.kernel.org
Subject: Re: [PATCH 2/7] sh_eth: RX checksum offload support
Hi Sergei,
On Sun, Jan 27, 2019 at 08:37:33PM +0300, Sergei Shtylyov wrote:
> Add support for the RX checksum offload. This is enabled by default and
> may be disabled and re-enabled using 'ethtool':
>
> # ethtool -K eth0 rx {on|off}
>
> Some Ether MACs provide a simple checksumming scheme which appears to be
> completely compatible with CHECKSUM_COMPLETE: sum of all packet data after
> the L2 header is appended to packet data; this may be trivially read by
> the driver and used to update the skb accordingly. The same checksumming
> scheme is implemented in the EtherAVB MACs and now supported by tha 'ravb'
> driver.
>
> In terms of performance, throughput is close to gigabit line rate with the
> RX checksum offload both enabled and disabled. The 'perf' output, however,
> appears to indicate that significantly less time is spent in do_csum() --
> this is as expected.
Nice.
FYI, this seems similar to what I observed for RAVB, perhaps on H3 I don't
exactly recall. On E3, which has less CPU power, I recently observed that
with rx-csum enabled I can achieve gigabit line rate, but with rx-csum
disabled throughput is significantly lower. I.e. on that system throughput
is CPU bound with 1500 byte packets unless rx-csum enabled.
Next point:
2da64300fbc ("ravb: expand rx descriptor data to accommodate hw checksum")
is fresh in my mind and I wonder if mdp->rx_buf_sz needs to grow to ensure
that there is always enough space for the csum. In particular, have you
tested this with MTU-size frames with VLANs. (My test is to run iperf3 over
a VLAN netdev, netperf over a VLAN netdev would likely work just as well.)
>
> Test results with RX checksum offload enabled:
>
> ~/netperf-2.2pl4# perf record -a ./netperf -t TCP_MAERTS -H 192.168.2.4
> TCP MAERTS TEST to 192.168.2.4
> Recv Send Send
> Socket Socket Message Elapsed
> Size Size Size Time Throughput
> bytes bytes bytes secs. 10^6bits/sec
>
> 131072 16384 16384 10.01 933.93
> [ perf record: Woken up 8 times to write data ]
> [ perf record: Captured and wrote 1.955 MB perf.data (41940 samples) ]
> ~/netperf-2.2pl4# perf report
> Samples: 41K of event 'cycles:ppp', Event count (approx.): 9915302763
> Overhead Command Shared Object Symbol
> 9.44% netperf [kernel.kallsyms] [k] __arch_copy_to_user
> 7.75% swapper [kernel.kallsyms] [k] _raw_spin_unlock_irq
> 6.31% swapper [kernel.kallsyms] [k] default_idle_call
> 5.89% swapper [kernel.kallsyms] [k] arch_cpu_idle
> 4.37% swapper [kernel.kallsyms] [k] tick_nohz_idle_exit
> 4.02% netperf [kernel.kallsyms] [k] _raw_spin_unlock_irq
> 2.52% netperf [kernel.kallsyms] [k] preempt_count_sub
> 1.81% netperf [kernel.kallsyms] [k] tcp_recvmsg
> 1.80% netperf [kernel.kallsyms] [k] _raw_spin_unlock_irqres
> 1.78% netperf [kernel.kallsyms] [k] preempt_count_add
> 1.36% netperf [kernel.kallsyms] [k] __tcp_transmit_skb
> 1.20% netperf [kernel.kallsyms] [k] __local_bh_enable_ip
> 1.10% netperf [kernel.kallsyms] [k] sh_eth_start_xmit
>
> Test results with RX checksum offload disabled:
>
> ~/netperf-2.2pl4# perf record -a ./netperf -t TCP_MAERTS -H 192.168.2.4
> TCP MAERTS TEST to 192.168.2.4
> Recv Send Send
> Socket Socket Message Elapsed
> Size Size Size Time Throughput
> bytes bytes bytes secs. 10^6bits/sec
> 131072 16384 16384 10.01 932.04
> [ perf record: Woken up 14 times to write data ]
> [ perf record: Captured and wrote 3.642 MB perf.data (78817 samples) ]
> ~/netperf-2.2pl4# perf report
> Samples: 78K of event 'cycles:ppp', Event count (approx.): 18091442796
> Overhead Command Shared Object Symbol
> 7.00% swapper [kernel.kallsyms] [k] do_csum
> 3.94% swapper [kernel.kallsyms] [k] sh_eth_poll
> 3.83% ksoftirqd/0 [kernel.kallsyms] [k] do_csum
> 3.23% swapper [kernel.kallsyms] [k] _raw_spin_unlock_irq
> 2.87% netperf [kernel.kallsyms] [k] __arch_copy_to_user
> 2.86% swapper [kernel.kallsyms] [k] arch_cpu_idle
> 2.13% swapper [kernel.kallsyms] [k] default_idle_call
> 2.12% ksoftirqd/0 [kernel.kallsyms] [k] sh_eth_poll
> 2.02% swapper [kernel.kallsyms] [k] _raw_spin_unlock_irqrestore
> 1.84% swapper [kernel.kallsyms] [k] __softirqentry_text_start
> 1.64% swapper [kernel.kallsyms] [k] tick_nohz_idle_exit
> 1.53% netperf [kernel.kallsyms] [k] _raw_spin_unlock_irq
> 1.32% netperf [kernel.kallsyms] [k] preempt_count_sub
> 1.27% swapper [kernel.kallsyms] [k] __pi___inval_dcache_area
> 1.22% swapper [kernel.kallsyms] [k] check_preemption_disabled
> 1.01% ksoftirqd/0 [kernel.kallsyms] [k] _raw_spin_unlock_irqrestore
>
> The above results collected on the R-Car V3H Starter Kit board.
>
> Based on the commit 4d86d3818627 ("ravb: RX checksum offload")...
>
> Signed-off-by: Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
>
> ---
> drivers/net/ethernet/renesas/sh_eth.c | 60 ++++++++++++++++++++++++++++++++--
> drivers/net/ethernet/renesas/sh_eth.h | 1
> 2 files changed, 59 insertions(+), 2 deletions(-)
>
> Index: net-next/drivers/net/ethernet/renesas/sh_eth.c
> ===================================================================
> --- net-next.orig/drivers/net/ethernet/renesas/sh_eth.c
> +++ net-next/drivers/net/ethernet/renesas/sh_eth.c
> @@ -1532,8 +1532,9 @@ static int sh_eth_dev_init(struct net_de
> mdp->irq_enabled = true;
> sh_eth_write(ndev, mdp->cd->eesipr_value, EESIPR);
>
> - /* PAUSE Prohibition */
> + /* EMAC Mode: PAUSE prohibition; Duplex; RX Checksum; TX; RX */
> sh_eth_write(ndev, ECMR_ZPF | (mdp->duplex ? ECMR_DM : 0) |
> + (ndev->features & NETIF_F_RXCSUM ? ECMR_RCSC : 0) |
> ECMR_TE | ECMR_RE, ECMR);
>
> if (mdp->cd->set_rate)
> @@ -1592,6 +1593,19 @@ static void sh_eth_dev_exit(struct net_d
> update_mac_address(ndev);
> }
>
> +static void sh_eth_rx_csum(struct sk_buff *skb)
> +{
> + u8 *hw_csum;
> +
> + /* The hardware checksum is 2 bytes appended to packet data */
> + if (unlikely(skb->len < sizeof(__sum16)))
> + return;
> + hw_csum = skb_tail_pointer(skb) - sizeof(__sum16);
> + skb->csum = csum_unfold((__force __sum16)get_unaligned_le16(hw_csum));
> + skb->ip_summed = CHECKSUM_COMPLETE;
> + skb_trim(skb, skb->len - sizeof(__sum16));
> +}
> +
> /* Packet receive function */
> static int sh_eth_rx(struct net_device *ndev, u32 intr_status, int *quota)
> {
> @@ -1666,6 +1680,8 @@ static int sh_eth_rx(struct net_device *
> DMA_FROM_DEVICE);
> skb_put(skb, pkt_len);
> skb->protocol = eth_type_trans(skb, ndev);
> + if (ndev->features & NETIF_F_RXCSUM)
> + sh_eth_rx_csum(skb);
> netif_receive_skb(skb);
> ndev->stats.rx_packets++;
> ndev->stats.rx_bytes += pkt_len;
> @@ -2921,6 +2937,39 @@ static void sh_eth_set_rx_mode(struct ne
> spin_unlock_irqrestore(&mdp->lock, flags);
> }
>
> +static void sh_eth_set_rx_csum(struct net_device *ndev, bool enable)
> +{
> + struct sh_eth_private *mdp = netdev_priv(ndev);
> + unsigned long flags;
> +
> + spin_lock_irqsave(&mdp->lock, flags);
> +
> + /* Disable TX and RX */
> + sh_eth_rcv_snd_disable(ndev);
> +
> + /* Modify RX Checksum setting */
> + sh_eth_modify(ndev, ECMR, ECMR_RCSC, enable ? ECMR_RCSC : 0);
> +
> + /* Enable TX and RX */
> + sh_eth_rcv_snd_enable(ndev);
> +
> + spin_unlock_irqrestore(&mdp->lock, flags);
> +}
> +
> +static int sh_eth_set_features(struct net_device *ndev,
> + netdev_features_t features)
> +{
> + netdev_features_t changed = ndev->features ^ features;
> + struct sh_eth_private *mdp = netdev_priv(ndev);
> +
> + if (changed & NETIF_F_RXCSUM && mdp->cd->rx_csum)
> + sh_eth_set_rx_csum(ndev, features & NETIF_F_RXCSUM);
> +
> + ndev->features = features;
> +
> + return 0;
> +}
> +
> static int sh_eth_get_vtag_index(struct sh_eth_private *mdp)
> {
> if (!mdp->port)
> @@ -3102,6 +3151,7 @@ static const struct net_device_ops sh_et
> .ndo_change_mtu = sh_eth_change_mtu,
> .ndo_validate_addr = eth_validate_addr,
> .ndo_set_mac_address = eth_mac_addr,
> + .ndo_set_features = sh_eth_set_features,
> };
>
> static const struct net_device_ops sh_eth_netdev_ops_tsu = {
> @@ -3117,6 +3167,7 @@ static const struct net_device_ops sh_et
> .ndo_change_mtu = sh_eth_change_mtu,
> .ndo_validate_addr = eth_validate_addr,
> .ndo_set_mac_address = eth_mac_addr,
> + .ndo_set_features = sh_eth_set_features,
> };
>
> #ifdef CONFIG_OF
> @@ -3245,6 +3296,11 @@ static int sh_eth_drv_probe(struct platf
> ndev->max_mtu = 2000 - (ETH_HLEN + VLAN_HLEN + ETH_FCS_LEN);
> ndev->min_mtu = ETH_MIN_MTU;
>
> + if (mdp->cd->rx_csum) {
> + ndev->features = NETIF_F_RXCSUM;
> + ndev->hw_features = NETIF_F_RXCSUM;
> + }
> +
> /* set function */
> if (mdp->cd->tsu)
> ndev->netdev_ops = &sh_eth_netdev_ops_tsu;
> @@ -3294,7 +3350,7 @@ static int sh_eth_drv_probe(struct platf
> goto out_release;
> }
> mdp->port = port;
> - ndev->features = NETIF_F_HW_VLAN_CTAG_FILTER;
> + ndev->features |= NETIF_F_HW_VLAN_CTAG_FILTER;
>
> /* Need to init only the first port of the two sharing a TSU */
> if (port == 0) {
> Index: net-next/drivers/net/ethernet/renesas/sh_eth.h
> ===================================================================
> --- net-next.orig/drivers/net/ethernet/renesas/sh_eth.h
> +++ net-next/drivers/net/ethernet/renesas/sh_eth.h
> @@ -500,6 +500,7 @@ struct sh_eth_cpu_data {
> unsigned no_xdfar:1; /* E-DMAC DOES NOT have RDFAR/TDFAR */
> unsigned xdfar_rw:1; /* E-DMAC has writeable RDFAR/TDFAR */
> unsigned csmr:1; /* E-DMAC has CSMR */
> + unsigned rx_csum:1; /* EtherC has ECMR.RCSC */
> unsigned select_mii:1; /* EtherC has RMII_MII (MII select register) */
> unsigned rmiimode:1; /* EtherC has RMIIMODE register */
> unsigned rtrate:1; /* EtherC has RTRATE register */
>
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