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From: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
To: Chengchang Tang <tangchengchang@huawei.com>, dev@dpdk.org
Cc: linuxarm@huawei.com, chas3@att.com, humin29@huawei.com,
	ferruh.yigit@intel.com, konstantin.ananyev@intel.com
Subject: Re: [dpdk-dev] [PATCH 1/2] net/bonding: support Tx prepare for bonding
Date: Tue, 8 Jun 2021 12:49:38 +0300
Message-ID: <4ce1752a-b605-8f35-ab06-13a671ef0e6c@oktetlabs.ru> (raw)
In-Reply-To: <1619171202-28486-2-git-send-email-tangchengchang@huawei.com>

"for bonding" is redundant in the summary since it is already "net/bonding".

On 4/23/21 12:46 PM, Chengchang Tang wrote:
> To use the HW offloads capability (e.g. checksum and TSO) in the Tx
> direction, the upper-layer users need to call rte_eth_dev_prepare to do
> some adjustment to the packets before sending them (e.g. processing
> pseudo headers when Tx checksum offoad enabled). But, the tx_prepare
> callback of the bond driver is not implemented. Therefore, related
> offloads can not be used unless the upper layer users process the packet
> properly in their own application. But it is bad for the
> transplantability.
> 
> However, it is difficult to design the tx_prepare callback for bonding
> driver. Because when a bonded device sends packets, the bonded device
> allocates the packets to different slave devices based on the real-time
> link status and bonding mode. That is, it is very difficult for the
> bonding device to determine which slave device's prepare function should
> be invoked. In addition, if the link status changes after the packets are
> prepared, the packets may fail to be sent because packets allocation may
> change.
> 
> So, in this patch, the tx_prepare callback of bonding driver is not
> implemented. Instead, the rte_eth_dev_tx_prepare() will be called for
> all the fast path packet in mode 0, 1, 2, 4, 5, 6. In this way, all
> tx_offloads can be processed correctly for all NIC devices in these modes.
> If tx_prepare is not required in some cases, then slave PMDs tx_prepare
> pointer should be NULL and rte_eth_tx_prepare() will be just a NOOP.
> In these cases, the impact on performance will be very limited. It is
> the responsibility of the slave PMDs to decide when the real tx_prepare
> needs to be used. The information from dev_config/queue_setup is
> sufficient for them to make these decisions.
> 
> Note:
> The rte_eth_tx_prepare is not added to bond mode 3(Broadcast). This is
> because in broadcast mode, a packet needs to be sent by all slave ports.
> Different PMDs process the packets differently in tx_prepare. As a result,
> the sent packet may be incorrect.
> 
> Signed-off-by: Chengchang Tang <tangchengchang@huawei.com>
> ---
>  drivers/net/bonding/rte_eth_bond.h     |  1 -
>  drivers/net/bonding/rte_eth_bond_pmd.c | 28 ++++++++++++++++++++++++----
>  2 files changed, 24 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/bonding/rte_eth_bond.h b/drivers/net/bonding/rte_eth_bond.h
> index 874aa91..1e6cc6d 100644
> --- a/drivers/net/bonding/rte_eth_bond.h
> +++ b/drivers/net/bonding/rte_eth_bond.h
> @@ -343,7 +343,6 @@ rte_eth_bond_link_up_prop_delay_set(uint16_t bonded_port_id,
>  int
>  rte_eth_bond_link_up_prop_delay_get(uint16_t bonded_port_id);
> 
> -
>  #ifdef __cplusplus
>  }
>  #endif
> diff --git a/drivers/net/bonding/rte_eth_bond_pmd.c b/drivers/net/bonding/rte_eth_bond_pmd.c
> index 2e9cea5..84af348 100644
> --- a/drivers/net/bonding/rte_eth_bond_pmd.c
> +++ b/drivers/net/bonding/rte_eth_bond_pmd.c
> @@ -606,8 +606,14 @@ bond_ethdev_tx_burst_round_robin(void *queue, struct rte_mbuf **bufs,
>  	/* Send packet burst on each slave device */
>  	for (i = 0; i < num_of_slaves; i++) {
>  		if (slave_nb_pkts[i] > 0) {
> +			int nb_prep_pkts;
> +
> +			nb_prep_pkts = rte_eth_tx_prepare(slaves[i],
> +					bd_tx_q->queue_id, slave_bufs[i],
> +					slave_nb_pkts[i]);
> +

Shouldn't it be called iff queue Tx offloads are not zero?
It will allow to decrease performance degradation if no
Tx offloads are enabled. Same in all cases below.

>  			num_tx_slave = rte_eth_tx_burst(slaves[i], bd_tx_q->queue_id,
> -					slave_bufs[i], slave_nb_pkts[i]);
> +					slave_bufs[i], nb_prep_pkts);

In fact it is a problem here and really big problems.
Tx prepare may fail and return less packets. Tx prepare
of some packet may always fail. If application tries to
send packets in a loop until success, it will be a
forever loop here. Since application calls Tx burst,
it is 100% legal behaviour of the function to return 0
if Tx ring is full. It is not an error indication.
However, in the case of Tx prepare it is an error
indication.

Should we change Tx burst description and enforce callers
to check for rte_errno? It sounds like a major change...

[snip]

  reply	other threads:[~2021-06-08  9:49 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-16 11:04 [dpdk-dev] [RFC 0/2] add Tx prepare support for bonding device Chengchang Tang
2021-04-16 11:04 ` [dpdk-dev] [RFC 1/2] net/bonding: add Tx prepare for bonding Chengchang Tang
2021-04-16 11:04 ` [dpdk-dev] [RFC 2/2] app/testpmd: add cmd for bonding Tx prepare Chengchang Tang
2021-04-16 11:12 ` [dpdk-dev] [RFC 0/2] add Tx prepare support for bonding device Min Hu (Connor)
2021-04-20  1:26 ` Ferruh Yigit
2021-04-20  2:44   ` Chengchang Tang
2021-04-20  8:33     ` Ananyev, Konstantin
2021-04-20 12:44       ` Chengchang Tang
2021-04-20 13:18         ` Ananyev, Konstantin
2021-04-20 14:06           ` Chengchang Tang
2021-04-23  9:46 ` [dpdk-dev] [PATCH " Chengchang Tang
2021-04-23  9:46   ` [dpdk-dev] [PATCH 1/2] net/bonding: support Tx prepare for bonding Chengchang Tang
2021-06-08  9:49     ` Andrew Rybchenko [this message]
2021-06-09  6:42       ` Chengchang Tang
2021-06-09  9:35         ` Andrew Rybchenko
2021-06-10  7:32           ` Chengchang Tang
2021-06-14 14:16             ` Andrew Rybchenko
2021-06-09 10:25         ` Ananyev, Konstantin
2021-06-10  6:46           ` Chengchang Tang
2021-06-14 11:36             ` Ananyev, Konstantin
2021-04-23  9:46   ` [dpdk-dev] [PATCH 2/2] net/bonding: support configuring Tx offloading " Chengchang Tang
2021-06-08  9:49     ` Andrew Rybchenko
2021-06-09  6:57       ` Chengchang Tang
2021-06-09  9:11         ` Ananyev, Konstantin
2021-06-09  9:37           ` Andrew Rybchenko
2021-06-10  6:29             ` Chengchang Tang
2021-06-14 11:05               ` Ananyev, Konstantin
2021-06-14 14:13                 ` Andrew Rybchenko
2021-04-30  6:26   ` [dpdk-dev] [PATCH 0/2] add Tx prepare support for bonding device Chengchang Tang
2021-04-30  6:47     ` Min Hu (Connor)
2021-06-03  1:44   ` Chengchang Tang

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