DPDK patches and discussions
 help / color / mirror / Atom feed
From: "Ananyev, Konstantin" <konstantin.ananyev@intel.com>
To: Chengchang Tang <tangchengchang@huawei.com>,
	Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>,
	"dev@dpdk.org" <dev@dpdk.org>
Cc: "linuxarm@huawei.com" <linuxarm@huawei.com>,
	"chas3@att.com" <chas3@att.com>,
	"humin29@huawei.com" <humin29@huawei.com>,
	"Yigit, Ferruh" <ferruh.yigit@intel.com>
Subject: Re: [dpdk-dev] [PATCH 1/2] net/bonding: support Tx prepare for bonding
Date: Mon, 14 Jun 2021 11:36:43 +0000
Message-ID: <DM6PR11MB4491E939218CE14104647EBD9A319@DM6PR11MB4491.namprd11.prod.outlook.com> (raw)
In-Reply-To: <f7098e21-d94a-9d0e-8e66-0bd6dd1e3152@huawei.com>


> On 2021/6/9 18:25, Ananyev, Konstantin wrote:
> >>> 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.
> >>
> >> Regarding this point, it has been discussed in the previous RFC:
> >> https://inbox.dpdk.org/dev/47f907cf-3933-1de9-9c45-6734b912eccd@huawei.com/
> >>
> >> According to the TX_OFFLOAD status of the current device, PMDs can determine
> >> whether tx_prepare is currently needed. If it is not needed, set pkt_tx_prepare
> >> to NULL, so that the actual tx_prepare processing will be skipped directly in
> >> rte_eth_tx_prepare().
> >>
> >>>
> >>>>  			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.
> >
> > Yes, that sounds like a problem and existing apps might be affected.
> >
> >>>
> >>> Should we change Tx burst description and enforce callers
> >>> to check for rte_errno? It sounds like a major change...
> >>>
> >
> > Agree, rte_errno for tx_burst() is probably a simplest and sanest way,
> > but yes, it is a change in behaviour and apps will need to be updated.
> > Another option for bond PMD - just silently free mbufs for which prepare()
> > fails (and probably update some stats counter).
> > Again it is a change in behaviour, but now just for one PMD, with tx offloads enabled.
> > Also as, I can see some tx_burst() function for that PMD already free packets silently:
> > bond_ethdev_tx_burst_alb(), bond_ethdev_tx_burst_broadcast().
> >
> > Actually another question - why the patch adds tx_prepare() only to some
> > TX modes but not all?
> > Is that itended?
> >
> 
> Yes. Currently, I have no ideal to perform tx_prepare() in broadcast mode with limited
> impact on performance. In broadcast mode, same packets will be send in several devices.
> In this process, we only update the ref_cnt of mbufs, but no copy of packets.
> As we know,
> tx_prepare() may change the data, so it may cause some problem if we perform tx_prepare()
> several times on the same packet.

You mean tx_prepare() for second dev can void changes made by tx_prepare() for first dev?
I suppose in theory it is possible, even if it is probably not the case right now in practise
(at least I am not aware about such cases).
Actually that's an interesting topic - same can happen even with user implementing multicast
on his own (see examples/ipv4_multicast/). 
I think these new limitations have to be documented clearly (at least).
Also probably  we need extra changes fo bond device dev_confgiure()/dev_get_info():
to check currently selected mode and based on that allow/reject tx offloads.
The question arises (again) how to figure out for which tx offloads dev->tx_prepare()
modifies the packet, for which not? 
Any thoughts here? 

> 
> >>
> >> I agree that if the failure is caused by Tx ring full, it is a legal behaviour.
> >> But what about the failure caused by other reasons? At present, it is possible
> >> for some PMDs to fail during tx_burst due to other reasons. In this case,
> >> repeated tries to send will also fail.
> >>
> >> I'm not sure if all PMDs need to support the behavior of sending packets in a
> >> loop until it succeeds. If not, I think the current problem can be reminded to
> >> the user by adding a description to the bonding. If it is necessary, I think the
> >> description of tx_burst should also add related instructions, so that the developers
> >> of PMDs can better understand how tx_burst should be designed, such as putting all
> >> hardware-related constraint checks into tx_prepare. And another prerequisite for
> >> the above behavior is that the packets must be prepared (i.e. checked by
> >> rte_eth_tx_prepare()). Otherwise, it may also fail to send. This means that we have
> >> to use rte_eth_tx_prepare() in more scenarios.
> >>
> >> What's Ferruh's opinion on this?
> >>
> >>> [snip]
> >>>
> >>> .
> >>>
> >


  reply	other threads:[~2021-06-14 11:36 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
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 [this message]
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=DM6PR11MB4491E939218CE14104647EBD9A319@DM6PR11MB4491.namprd11.prod.outlook.com \
    --to=konstantin.ananyev@intel.com \
    --cc=andrew.rybchenko@oktetlabs.ru \
    --cc=chas3@att.com \
    --cc=dev@dpdk.org \
    --cc=ferruh.yigit@intel.com \
    --cc=humin29@huawei.com \
    --cc=linuxarm@huawei.com \
    --cc=tangchengchang@huawei.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

DPDK patches and discussions

This inbox may be cloned and mirrored by anyone:

	git clone --mirror https://inbox.dpdk.org/dev/0 dev/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 dev dev/ https://inbox.dpdk.org/dev \
		dev@dpdk.org
	public-inbox-index dev

Example config snippet for mirrors.
Newsgroup available over NNTP:
	nntp://inbox.dpdk.org/inbox.dpdk.dev


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git