[dpdk-dev] [PATCH v1] ethdev: introduce shared Rx queue

Xueming(Steven) Li xuemingl at nvidia.com
Wed Aug 11 14:59:19 CEST 2021
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> -----Original Message-----
> From: Ferruh Yigit <ferruh.yigit at intel.com>
> Sent: Wednesday, August 11, 2021 8:04 PM
> To: Xueming(Steven) Li <xuemingl at nvidia.com>; Jerin Jacob <jerinjacobk at gmail.com>
> Cc: dpdk-dev <dev at dpdk.org>; NBU-Contact-Thomas Monjalon <thomas at monjalon.net>; Andrew Rybchenko
> <andrew.rybchenko at oktetlabs.ru>
> Subject: Re: [dpdk-dev] [PATCH v1] ethdev: introduce shared Rx queue
> 
> On 8/11/2021 9:28 AM, Xueming(Steven) Li wrote:
> >
> >
> >> -----Original Message-----
> >> From: Jerin Jacob <jerinjacobk at gmail.com>
> >> Sent: Wednesday, August 11, 2021 4:03 PM
> >> To: Xueming(Steven) Li <xuemingl at nvidia.com>
> >> Cc: dpdk-dev <dev at dpdk.org>; Ferruh Yigit <ferruh.yigit at intel.com>;
> >> NBU-Contact-Thomas Monjalon <thomas at monjalon.net>; Andrew Rybchenko
> >> <andrew.rybchenko at oktetlabs.ru>
> >> Subject: Re: [dpdk-dev] [PATCH v1] ethdev: introduce shared Rx queue
> >>
> >> On Mon, Aug 9, 2021 at 7:46 PM Xueming(Steven) Li <xuemingl at nvidia.com> wrote:
> >>>
> >>> Hi,
> >>>
> >>>> -----Original Message-----
> >>>> From: Jerin Jacob <jerinjacobk at gmail.com>
> >>>> Sent: Monday, August 9, 2021 9:51 PM
> >>>> To: Xueming(Steven) Li <xuemingl at nvidia.com>
> >>>> Cc: dpdk-dev <dev at dpdk.org>; Ferruh Yigit <ferruh.yigit at intel.com>;
> >>>> NBU-Contact-Thomas Monjalon <thomas at monjalon.net>; Andrew Rybchenko
> >>>> <andrew.rybchenko at oktetlabs.ru>
> >>>> Subject: Re: [dpdk-dev] [PATCH v1] ethdev: introduce shared Rx
> >>>> queue
> >>>>
> >>>> On Mon, Aug 9, 2021 at 5:18 PM Xueming Li <xuemingl at nvidia.com> wrote:
> >>>>>
> >>>>> In current DPDK framework, each RX queue is pre-loaded with mbufs
> >>>>> for incoming packets. When number of representors scale out in a
> >>>>> switch domain, the memory consumption became significant. Most
> >>>>> important, polling all ports leads to high cache miss, high
> >>>>> latency and low throughput.
> >>>>>
> >>>>> This patch introduces shared RX queue. Ports with same
> >>>>> configuration in a switch domain could share RX queue set by specifying sharing group.
> >>>>> Polling any queue using same shared RX queue receives packets from
> >>>>> all member ports. Source port is identified by mbuf->port.
> >>>>>
> >>>>> Port queue number in a shared group should be identical. Queue
> >>>>> index is
> >>>>> 1:1 mapped in shared group.
> >>>>>
> >>>>> Share RX queue is supposed to be polled on same thread.
> >>>>>
> >>>>> Multiple groups is supported by group ID.
> >>>>
> >>>> Is this offload specific to the representor? If so can this name be changed specifically to representor?
> >>>
> >>> Yes, PF and representor in switch domain could take advantage.
> >>>
> >>>> If it is for a generic case, how the flow ordering will be maintained?
> >>>
> >>> Not quite sure that I understood your question. The control path of
> >>> is almost same as before, PF and representor port still needed, rte flows not impacted.
> >>> Queues still needed for each member port, descriptors(mbuf) will be
> >>> supplied from shared Rx queue in my PMD implementation.
> >>
> >> My question was if create a generic RTE_ETH_RX_OFFLOAD_SHARED_RXQ
> >> offload, multiple ethdev receive queues land into the same receive queue, In that case, how the flow order is maintained for
> respective receive queues.
> >
> > I guess the question is testpmd forward stream? The forwarding logic has to be changed slightly in case of shared rxq.
> > basically for each packet in rx_burst result, lookup source stream according to mbuf->port, forwarding to target fs.
> > Packets from same source port could be grouped as a small burst to
> > process, this will accelerates the performance if traffic come from
> > limited ports. I'll introduce some common api to do shard rxq forwarding, call it with packets handling callback, so it suites for all
> forwarding engine. Will sent patches soon.
> >
> 
> All ports will put the packets in to the same queue (share queue), right? Does this means only single core will poll only, what will
> happen if there are multiple cores polling, won't it cause problem?

This has been mentioned in commit log, the shared rxq is supposed to be polling in single thread(core) - I think it should be "MUST".
Result is unexpected if there are multiple cores pooling, that's why I added a polling schedule check in testpmd.
Similar for rx/tx burst function, a queue can't be polled on multiple thread(core), and for performance concern, no such check in eal api.

If users want to utilize multiple cores to distribute workloads, it's possible to define more groups, queues in different group could be
could be polled on multiple cores.

It's possible to poll every member port in group, but not necessary, any port in group could be polled to get packets for all ports in group.

If the member port subject to hot plug/remove,  it's possible to create a vdev with same queue number, copy rxq object and poll vdev
as a dedicate proxy for the group.

> 
> And if this requires specific changes in the application, I am not sure about the solution, can't this work in a transparent way to the
> application?

Yes, we considered different options in design stage. One possible solution is to cache received packets in rings, this can be done on
eth layer, but I'm afraid less benefits, user still has to be a ware of multiple core polling. 
This can be done as a wrapper PMD later, more efforts.

> 
> Overall, is this for optimizing memory for the port represontors? If so can't we have a port representor specific solution, reducing
> scope can reduce the complexity it brings?

This feature supports both PF and representor, and yes, major issue is memory of representors. Poll all representors also 
introduces more core cache miss latency. This feature essentially aggregates all ports in group as one port.
On the other hand, it's useful for rte flow to create offloading flows using representor as a regular port ID.

It's great if any new solution/suggestion, my head buried in PMD code :)

> 
> >> If this offload is only useful for representor case, Can we make this
> >> offload specific to representor the case by changing its name and scope.
> >
> > It works for both PF and representors in same switch domain, for application like OVS, few changes to apply.
> >
> >>
> >>
> >>>
> >>>>
> >>>>>
> >>>>> Signed-off-by: Xueming Li <xuemingl at nvidia.com>
> >>>>> ---
> >>>>>  doc/guides/nics/features.rst                    | 11 +++++++++++
> >>>>>  doc/guides/nics/features/default.ini            |  1 +
> >>>>>  doc/guides/prog_guide/switch_representation.rst | 10 ++++++++++
> >>>>>  lib/ethdev/rte_ethdev.c                         |  1 +
> >>>>>  lib/ethdev/rte_ethdev.h                         |  7 +++++++
> >>>>>  5 files changed, 30 insertions(+)
> >>>>>
> >>>>> diff --git a/doc/guides/nics/features.rst
> >>>>> b/doc/guides/nics/features.rst index a96e12d155..2e2a9b1554 100644
> >>>>> --- a/doc/guides/nics/features.rst
> >>>>> +++ b/doc/guides/nics/features.rst
> >>>>> @@ -624,6 +624,17 @@ Supports inner packet L4 checksum.
> >>>>>    ``tx_offload_capa,tx_queue_offload_capa:DEV_TX_OFFLOAD_OUTER_UDP_CKSUM``.
> >>>>>
> >>>>>
> >>>>> +.. _nic_features_shared_rx_queue:
> >>>>> +
> >>>>> +Shared Rx queue
> >>>>> +---------------
> >>>>> +
> >>>>> +Supports shared Rx queue for ports in same switch domain.
> >>>>> +
> >>>>> +* **[uses]     rte_eth_rxconf,rte_eth_rxmode**: ``offloads:RTE_ETH_RX_OFFLOAD_SHARED_RXQ``.
> >>>>> +* **[provides] mbuf**: ``mbuf.port``.
> >>>>> +
> >>>>> +
> >>>>>  .. _nic_features_packet_type_parsing:
> >>>>>
> >>>>>  Packet type parsing
> >>>>> diff --git a/doc/guides/nics/features/default.ini
> >>>>> b/doc/guides/nics/features/default.ini
> >>>>> index 754184ddd4..ebeb4c1851 100644
> >>>>> --- a/doc/guides/nics/features/default.ini
> >>>>> +++ b/doc/guides/nics/features/default.ini
> >>>>> @@ -19,6 +19,7 @@ Free Tx mbuf on demand =
> >>>>>  Queue start/stop     =
> >>>>>  Runtime Rx queue setup =
> >>>>>  Runtime Tx queue setup =
> >>>>> +Shared Rx queue      =
> >>>>>  Burst mode info      =
> >>>>>  Power mgmt address monitor =
> >>>>>  MTU update           =
> >>>>> diff --git a/doc/guides/prog_guide/switch_representation.rst
> >>>>> b/doc/guides/prog_guide/switch_representation.rst
> >>>>> index ff6aa91c80..45bf5a3a10 100644
> >>>>> --- a/doc/guides/prog_guide/switch_representation.rst
> >>>>> +++ b/doc/guides/prog_guide/switch_representation.rst
> >>>>> @@ -123,6 +123,16 @@ thought as a software "patch panel" front-end for applications.
> >>>>>  .. [1] `Ethernet switch device driver model (switchdev)
> >>>>>
> >>>>> <https://www.kernel.org/doc/Documentation/networking/switchdev.txt
> >>>>>> `_
> >>>>>
> >>>>> +- Memory usage of representors is huge when number of representor
> >>>>> +grows,
> >>>>> +  because PMD always allocate mbuf for each descriptor of Rx queue.
> >>>>> +  Polling the large number of ports brings more CPU load, cache
> >>>>> +miss and
> >>>>> +  latency. Shared Rx queue can be used to share Rx queue between
> >>>>> +PF and
> >>>>> +  representors in same switch domain.
> >>>>> +``RTE_ETH_RX_OFFLOAD_SHARED_RXQ``
> >>>>> +  is present in Rx offloading capability of device info. Setting
> >>>>> +the
> >>>>> +  offloading flag in device Rx mode or Rx queue configuration to
> >>>>> +enable
> >>>>> +  shared Rx queue. Polling any member port of shared Rx queue can
> >>>>> +return
> >>>>> +  packets of all ports in group, port ID is saved in ``mbuf.port``.
> >>>>> +
> >>>>>  Basic SR-IOV
> >>>>>  ------------
> >>>>>
> >>>>> diff --git a/lib/ethdev/rte_ethdev.c b/lib/ethdev/rte_ethdev.c
> >>>>> index 9d95cd11e1..1361ff759a 100644
> >>>>> --- a/lib/ethdev/rte_ethdev.c
> >>>>> +++ b/lib/ethdev/rte_ethdev.c
> >>>>> @@ -127,6 +127,7 @@ static const struct {
> >>>>>         RTE_RX_OFFLOAD_BIT2STR(OUTER_UDP_CKSUM),
> >>>>>         RTE_RX_OFFLOAD_BIT2STR(RSS_HASH),
> >>>>>         RTE_ETH_RX_OFFLOAD_BIT2STR(BUFFER_SPLIT),
> >>>>> +       RTE_ETH_RX_OFFLOAD_BIT2STR(SHARED_RXQ),
> >>>>>  };
> >>>>>
> >>>>>  #undef RTE_RX_OFFLOAD_BIT2STR
> >>>>> diff --git a/lib/ethdev/rte_ethdev.h b/lib/ethdev/rte_ethdev.h
> >>>>> index d2b27c351f..a578c9db9d 100644
> >>>>> --- a/lib/ethdev/rte_ethdev.h
> >>>>> +++ b/lib/ethdev/rte_ethdev.h
> >>>>> @@ -1047,6 +1047,7 @@ struct rte_eth_rxconf {
> >>>>>         uint8_t rx_drop_en; /**< Drop packets if no descriptors are available. */
> >>>>>         uint8_t rx_deferred_start; /**< Do not start queue with rte_eth_dev_start(). */
> >>>>>         uint16_t rx_nseg; /**< Number of descriptions in rx_seg array.
> >>>>> */
> >>>>> +       uint32_t shared_group; /**< Shared port group index in
> >>>>> + switch domain. */
> >>>>>         /**
> >>>>>          * Per-queue Rx offloads to be set using DEV_RX_OFFLOAD_* flags.
> >>>>>          * Only offloads set on rx_queue_offload_capa or
> >>>>> rx_offload_capa @@ -1373,6 +1374,12 @@ struct rte_eth_conf {
> >>>>> #define DEV_RX_OFFLOAD_OUTER_UDP_CKSUM  0x00040000
> >>>>>  #define DEV_RX_OFFLOAD_RSS_HASH                0x00080000
> >>>>>  #define RTE_ETH_RX_OFFLOAD_BUFFER_SPLIT 0x00100000
> >>>>> +/**
> >>>>> + * Rx queue is shared among ports in same switch domain to save
> >>>>> +memory,
> >>>>> + * avoid polling each port. Any port in group can be used to receive packets.
> >>>>> + * Real source port number saved in mbuf->port field.
> >>>>> + */
> >>>>> +#define RTE_ETH_RX_OFFLOAD_SHARED_RXQ   0x00200000
> >>>>>
> >>>>>  #define DEV_RX_OFFLOAD_CHECKSUM (DEV_RX_OFFLOAD_IPV4_CKSUM | \
> >>>>>                                  DEV_RX_OFFLOAD_UDP_CKSUM | \
> >>>>> --
> >>>>> 2.25.1
> >>>>>
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