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From: Chas Williams <3chas3@gmail.com>
To: fengchengwen <fengchengwen@huawei.com>,
	Ferruh Yigit <ferruh.yigit@xilinx.com>,
	thomas@monjalon.net, andrew.rybchenko@oktetlabs.ru,
	konstantin.ananyev@intel.com
Cc: dev@dpdk.org, chas3@att.com, humin29@huawei.com
Subject: Re: [PATCH v2 1/3] net/bonding: support Tx prepare
Date: Sat, 17 Sep 2022 09:38:29 -0400
Message-ID: <863016bd-a20b-8a9f-8edc-cfddc0593546@gmail.com> (raw)
In-Reply-To: <509a1984-841a-e42c-05c1-707b024ef7a8@huawei.com>



On 9/16/22 22:35, fengchengwen wrote:
> Hi Chas,
> 
> On 2022/9/15 0:59, Chas Williams wrote:
>> On 9/13/22 20:46, fengchengwen wrote:
>>>
>>> The main problem is hard to design a tx_prepare for bonding device:
>>> 1. as Chas Williams said, there maybe twice hash calc to get target slave
>>>      devices.
>>> 2. also more important, if the slave devices have changes(e.g. slave device
>>>      link down or remove), and if the changes happens between bond-tx-prepare and
>>>      bond-tx-burst, the output slave will changes, and this may lead to checksum
>>>      failed. (Note: a bond device with slave devices may from different vendors,
>>>      and slave devices may have different requirements, e.g. slave-A support calc
>>>      IPv4 pseudo-head automatic (no need driver pre-calc), but slave-B need driver
>>>      pre-calc).
>>>
>>> Current design cover the above two scenarios by using in-place tx-prepare. and
>>> in addition, bond devices are not transparent to applications, I think it's a
>>> practical method to provide tx-prepare support in this way.
>>>
>>
>>
>> I don't think you need to export an enable/disable routine for the use of
>> rte_eth_tx_prepare. It's safe to just call that routine, even if it isn't
>> implemented. You are just trading one branch in DPDK librte_eth_dev for a
>> branch in drivers/net/bonding.
> 
> Our first patch was just like yours (just add tx-prepare default), but community
> is concerned about impacting performance.
> 
> As a trade-off, I think we can add the enable/disable API.

IMHO, that's a bad idea. If the rte_eth_dev_tx_prepare API affects
performance adversly, that is not a bonding problem. All applications
should be calling rte_eth_dev_tx_prepare. There's no defined API
to determine if rte_eth_dev_tx_prepare should be called. Therefore,
applications should always call rte_eth_dev_tx_prepare. Regardless,
as I previously mentioned, you are just trading the location of
the branch, especially in the bonding case.

If rte_eth_dev_tx_prepare is causing a performance drop, then that API
should be improved or rewritten. There are PMD that require you to use
that API. Locally, we had maintained a patch to eliminate the use of
rte_eth_dev_tx_prepare. However, that has been getting harder and harder
to maintain. The performance lost by just calling rte_eth_dev_tx_prepare
was marginal.

> 
>>
>> I think you missed fixing tx_machine in 802.3ad support. We have been using
>> the following patch locally which I never got around to submitting.
> 
> You are right, I will send V3 fix it.
> 
>>
>>
>>  From a458654d68ff5144266807ef136ac3dd2adfcd98 Mon Sep 17 00:00:00 2001
>> From: "Charles (Chas) Williams" <chwillia@ciena.com>
>> Date: Tue, 3 May 2022 16:52:37 -0400
>> Subject: [PATCH] net/bonding: call rte_eth_tx_prepare before rte_eth_tx_burst
>>
>> Some PMDs might require a call to rte_eth_tx_prepare before sending the
>> packets for transmission. Typically, the prepare step handles the VLAN
>> headers, but it may need to do other things.
>>
>> Signed-off-by: Chas Williams <chwillia@ciena.com>
> 
> ...
> 
>>                * ring if transmission fails so the packet isn't lost.
>> @@ -1322,8 +1350,12 @@ bond_ethdev_tx_burst_broadcast(void *queue, struct rte_mbuf **bufs,
>>   
>>       /* Transmit burst on each active slave */
>>       for (i = 0; i < num_of_slaves; i++) {
>> -        slave_tx_total[i] = rte_eth_tx_burst(slaves[i], bd_tx_q->queue_id,
>> +        uint16_t nb_prep;
>> +
>> +        nb_prep = rte_eth_tx_prepare(slaves[i], bd_tx_q->queue_id,
>>                       bufs, nb_pkts);
>> +        slave_tx_total[i] = rte_eth_tx_burst(slaves[i], bd_tx_q->queue_id,
>> +                    bufs, nb_prep);
> 
> The tx-prepare may edit packet data, and the broadcast mode will send a packet to all slaves,
> the packet data is sent and edited at the same time. Is this likely to cause problems ?

This routine is already broken. You can't just increment the refcount
and send the packet into a PMD's transmit routine. Nothing guarantees
that a transmit routine will not modify the packet. Many PMDs perform an
rte_vlan_insert. You should at least perform a clone of the packet so
that the mbuf headers aren't mangled by each PMD. Just to be safe you
should perform a partial deep copy of the packet headers in case some
PMD does an rte_vlan_insert and the other PMDs in the bonding group do
not need an rte_vlan_insert.

So doing a blind rte_eth_dev_tx_preprare isn't making anything much
worse.

> 
>>   
>>           if (unlikely(slave_tx_total[i] < nb_pkts))
>>               tx_failed_flag = 1;

  reply	other threads:[~2022-09-17 13:38 UTC|newest]

Thread overview: 61+ 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
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
2022-05-24 12:11       ` Min Hu (Connor)
2022-07-25  4:08     ` [PATCH v2 0/3] add Tx prepare support for bonding driver Chengwen Feng
2022-07-25  4:08       ` [PATCH v2 1/3] net/bonding: support Tx prepare Chengwen Feng
2022-09-13 10:22         ` Ferruh Yigit
2022-09-13 15:08           ` Chas Williams
2022-09-14  0:46           ` fengchengwen
2022-09-14 16:59             ` Chas Williams
2022-09-17  2:35               ` fengchengwen
2022-09-17 13:38                 ` Chas Williams [this message]
2022-09-19 14:07                   ` Konstantin Ananyev
2022-09-19 23:02                     ` Chas Williams
2022-09-22  2:12                       ` fengchengwen
2022-09-25 10:32                         ` Chas Williams
2022-09-26 10:18                       ` Konstantin Ananyev
2022-09-26 16:36                         ` Chas Williams
2022-07-25  4:08       ` [PATCH v2 2/3] net/bonding: support Tx prepare fail stats Chengwen Feng
2022-07-25  4:08       ` [PATCH v2 3/3] net/bonding: add testpmd cmd for Tx prepare Chengwen Feng
2022-07-25  7:04       ` [PATCH v2 0/3] add Tx prepare support for bonding driver humin (Q)
2022-09-13  1:41       ` fengchengwen
2022-09-17  4:15     ` [PATCH v3 " Chengwen Feng
2022-09-17  4:15       ` [PATCH v3 1/3] net/bonding: support Tx prepare Chengwen Feng
2022-09-17  4:15       ` [PATCH v3 2/3] net/bonding: support Tx prepare fail stats Chengwen Feng
2022-09-17  4:15       ` [PATCH v3 3/3] net/bonding: add testpmd cmd for Tx prepare Chengwen Feng
2022-10-09  3:36     ` [PATCH v4] net/bonding: call Tx prepare before Tx burst Chengwen Feng
2022-10-10 19:42       ` Chas Williams
2022-10-11 13:28         ` fengchengwen
2022-10-11 13:20     ` [PATCH v5] " Chengwen Feng
2022-10-15 15:26       ` Chas Williams
2022-10-18 14:25         ` fengchengwen
2022-10-20  7:07         ` Andrew Rybchenko
2021-04-23  9:46   ` [dpdk-dev] [PATCH 2/2] net/bonding: support configuring Tx offloading for bonding 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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