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Date: Mon, 25 Mar 2024 19:29:04 -0700
From: Vinicius Costa Gomes <vinicius.gomes@...el.com>
To: Song Yoong Siang <yoong.siang.song@...el.com>, Jesse Brandeburg
<jesse.brandeburg@...el.com>, Tony Nguyen <anthony.l.nguyen@...el.com>,
"David S . Miller" <davem@...emloft.net>, Eric
Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo
Abeni <pabeni@...hat.com>, Richard Cochran <richardcochran@...il.com>,
Alexei
Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
Jesper Dangaard Brouer <hawk@...nel.org>, John Fastabend
<john.fastabend@...il.com>, Stanislav Fomichev <sdf@...gle.com>, Florian
Bezdeka <florian.bezdeka@...mens.com>, Kurt Kanzenbach
<kurt@...utronix.de>, Maciej
Fijalkowski <maciej.fijalkowski@...el.com>
Cc: intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
xdp-hints@...-project.net
Subject: Re: [PATCH iwl-next,v4 1/1] igc: Add Tx hardware timestamp request
for AF_XDP zero-copy packet
Song Yoong Siang <yoong.siang.song@...el.com> writes:
> This patch adds support to per-packet Tx hardware timestamp request to
> AF_XDP zero-copy packet via XDP Tx metadata framework. Please note that
> user needs to enable Tx HW timestamp capability via igc_ioctl() with
> SIOCSHWTSTAMP cmd before sending xsk Tx hardware timestamp request.
>
> Same as implementation in RX timestamp XDP hints kfunc metadata, Timer 0
> (adjustable clock) is used in xsk Tx hardware timestamp. i225/i226 have
> four sets of timestamping registers. *skb and *xsk_tx_buffer pointers
> are used to indicate whether the timestamping register is already occupied.
>
> Furthermore, a boolean variable named xsk_pending_ts is used to hold the
> transmit completion until the tx hardware timestamp is ready. This is
> because, for i225/i226, the timestamp notification event comes some time
> after the transmit completion event. The driver will retrigger hardware irq
> to clean the packet after retrieve the tx hardware timestamp.
>
> Besides, xsk_meta is added into struct igc_tx_timestamp_request as a hook
> to the metadata location of the transmit packet. When the Tx timestamp
> interrupt is fired, the interrupt handler will copy the value of Tx hwts
> into metadata location via xsk_tx_metadata_complete().
>
> This patch is tested with tools/testing/selftests/bpf/xdp_hw_metadata
> on Intel ADL-S platform. Below are the test steps and results.
>
> Test Step 1: Run xdp_hw_metadata app
> ./xdp_hw_metadata <iface> > /dev/shm/result.log
>
> Test Step 2: Enable Tx hardware timestamp
> hwstamp_ctl -i <iface> -t 1 -r 1
>
> Test Step 3: Run ptp4l and phc2sys for time synchronization
>
> Test Step 4: Generate UDP packets with 1ms interval for 10s
> trafgen --dev <iface> '{eth(da=<addr>), udp(dp=9091)}' -t 1ms -n 10000
>
> Test Step 5: Rerun Step 1-3 with 10s iperf3 as background traffic
>
> Test Step 6: Rerun Step 1-4 with 10s iperf3 as background traffic
>
> Based on iperf3 results below, the impact of holding tx completion to
> throughput is not observable.
>
> Result of last UDP packet (no. 10000) in Step 4:
> poll: 1 (0) skip=99 fail=0 redir=10000
> xsk_ring_cons__peek: 1
> 0x5640a37972d0: rx_desc[9999]->addr=f2110 addr=f2110 comp_addr=f2110 EoP
> rx_hash: 0x2049BE1D with RSS type:0x1
> HW RX-time: 1679819246792971268 (sec:1679819246.7930) delta to User RX-time sec:0.0000 (14.990 usec)
> XDP RX-time: 1679819246792981987 (sec:1679819246.7930) delta to User RX-time sec:0.0000 (4.271 usec)
> No rx_vlan_tci or rx_vlan_proto, err=-95
> 0x5640a37972d0: ping-pong with csum=ab19 (want 315b) csum_start=34 csum_offset=6
> 0x5640a37972d0: complete tx idx=9999 addr=f010
> HW TX-complete-time: 1679819246793036971 (sec:1679819246.7930) delta to User TX-complete-time sec:0.0001 (77.656 usec)
> XDP RX-time: 1679819246792981987 (sec:1679819246.7930) delta to User TX-complete-time sec:0.0001 (132.640 usec)
> HW RX-time: 1679819246792971268 (sec:1679819246.7930) delta to HW TX-complete-time sec:0.0001 (65.703 usec)
> 0x5640a37972d0: complete rx idx=10127 addr=f2110
>
> Result of iperf3 without tx hwts request in step 5:
> [ ID] Interval Transfer Bitrate Retr
> [ 5] 0.00-10.00 sec 2.74 GBytes 2.36 Gbits/sec 0 sender
> [ 5] 0.00-10.05 sec 2.74 GBytes 2.34 Gbits/sec receiver
>
> Result of iperf3 running parallel with trafgen command in step 6:
> [ ID] Interval Transfer Bitrate Retr
> [ 5] 0.00-10.00 sec 2.74 GBytes 2.36 Gbits/sec 0 sender
> [ 5] 0.00-10.04 sec 2.74 GBytes 2.34 Gbits/sec receiver
>
> Co-developed-by: Lai Peter Jun Ann <jun.ann.lai@...el.com>
> Signed-off-by: Lai Peter Jun Ann <jun.ann.lai@...el.com>
> Signed-off-by: Song Yoong Siang <yoong.siang.song@...el.com>
> Acked-by: John Fastabend <john.fastabend@...il.com>
> ---
> V1: https://patchwork.kernel.org/project/netdevbpf/patch/20231215162158.951925-1-yoong.siang.song@intel.com/
> V2: https://patchwork.kernel.org/project/netdevbpf/cover/20240301162348.898619-1-yoong.siang.song@intel.com/
> V3: https://patchwork.kernel.org/project/netdevbpf/cover/20240303083225.1184165-1-yoong.siang.song@intel.com/
>
> changelog:
> V1 -> V2
> - In struct igc_tx_timestamp_request, keep a pointer to igc_tx_buffer,
> instead of pointing xsk_pending_ts (Vinicius).
> - In struct igc_tx_timestamp_request, introduce buffer_type to indicate
> whether skb or igc_tx_buffer pointer should be use (Vinicius).
> - In struct igc_metadata_request, remove igc_adapter pointer (Vinicius).
> - When request tx hwts, copy the value of cmd_type, instead of using
> pointer (Vinicius).
> - For boolean variable, use true and false, instead of 1 and 0 (Vinicius).
> - In igc_xsk_request_timestamp(), make an early return if none of the 4 ts
> registers is available (Vinicius).
> - Create helper functions to clear tx buffer and skb for tstamp (John).
> - Perform throughput test with mix traffic (Vinicius & John).
> V2 -> V3
> - Improve tstamp reg searching loop for better readability (John).
> - In igc_ptp_free_tx_buffer(), add comment to inform user that
> tstamp->xsk_tx_buffer and tstamp->skb are in union (John).
> V3 -> V4
> - Add protection with xp_tx_metadata_enabled (Kurt & Maciej).
> ---
> ---
> drivers/net/ethernet/intel/igc/igc.h | 71 ++++++++------
> drivers/net/ethernet/intel/igc/igc_main.c | 113 ++++++++++++++++++++--
> drivers/net/ethernet/intel/igc/igc_ptp.c | 51 ++++++++--
> 3 files changed, 195 insertions(+), 40 deletions(-)
>
[...]
> diff --git a/drivers/net/ethernet/intel/igc/igc_ptp.c b/drivers/net/ethernet/intel/igc/igc_ptp.c
> index 885faaa7b9de..1bb026232efc 100644
> --- a/drivers/net/ethernet/intel/igc/igc_ptp.c
> +++ b/drivers/net/ethernet/intel/igc/igc_ptp.c
> @@ -11,6 +11,7 @@
> #include <linux/ktime.h>
> #include <linux/delay.h>
> #include <linux/iopoll.h>
> +#include <net/xdp_sock_drv.h>
>
> #define INCVALUE_MASK 0x7fffffff
> #define ISGN 0x80000000
> @@ -545,6 +546,30 @@ static void igc_ptp_enable_rx_timestamp(struct igc_adapter *adapter)
> wr32(IGC_TSYNCRXCTL, val);
> }
>
> +static void igc_ptp_free_tx_buffer(struct igc_adapter *adapter,
> + struct igc_tx_timestamp_request *tstamp)
> +{
> + if (tstamp->buffer_type == IGC_TX_BUFFER_TYPE_XSK) {
> + /* Release the transmit completion */
> + tstamp->xsk_tx_buffer->xsk_pending_ts = false;
> +
> + /* Note: tstamp->skb and tstamp->xsk_tx_buffer are in union.
> + * By setting tstamp->xsk_tx_buffer to NULL, tstamp->skb will
> + * become NULL as well.
> + */
> + tstamp->xsk_tx_buffer = NULL;
> + tstamp->buffer_type = 0;
> +
> + /* Trigger txrx interrupt for transmit completion */
> + igc_xsk_wakeup(adapter->netdev, tstamp->xsk_queue_index, 0);
> +
> + return;
> + }
> +
> + dev_kfree_skb_any(tstamp->skb);
> + tstamp->skb = NULL;
> +}
> +
> static void igc_ptp_clear_tx_tstamp(struct igc_adapter *adapter)
> {
> unsigned long flags;
> @@ -555,8 +580,8 @@ static void igc_ptp_clear_tx_tstamp(struct igc_adapter *adapter)
> for (i = 0; i < IGC_MAX_TX_TSTAMP_REGS; i++) {
> struct igc_tx_timestamp_request *tstamp = &adapter->tx_tstamp[i];
>
> - dev_kfree_skb_any(tstamp->skb);
> - tstamp->skb = NULL;
> + if (tstamp->skb)
> + igc_ptp_free_tx_buffer(adapter, tstamp);
> }
>
More a question: you are potentially triggering an interrupt from
igc_ptp_clear_tx_tstamp() (igc_xsk_wakeup()) which can be called from
igc_down(). So, how does it work when there's a pending timestamp and
you remove the igc module? (example of a situation that it might be
problematic).
Cheers,
--
Vinicius
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