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Message-ID: <144bf42b-8b9e-48b6-81f7-07af79cb0a94@linux.dev> Date: Fri, 6 Sep 2024 23:17:13 +0800 From: Zhu Yanjun <yanjun.zhu@...ux.dev> To: Edward Srouji <edwards@...dia.com>, Leon Romanovsky <leon@...nel.org>, Jason Gunthorpe <jgg@...dia.com> Cc: Leon Romanovsky <leonro@...dia.com>, linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org, netdev@...r.kernel.org, Saeed Mahameed <saeedm@...dia.com>, Tariq Toukan <tariqt@...dia.com>, Yishai Hadas <yishaih@...dia.com> Subject: Re: [PATCH rdma-next 0/2] Introduce mlx5 data direct placement (DDP) 在 2024/9/6 20:17, Edward Srouji 写道: > > On 9/6/2024 8:02 AM, Zhu Yanjun wrote: >> External email: Use caution opening links or attachments >> >> >> 在 2024/9/5 20:23, Edward Srouji 写道: >>> >>> On 9/4/2024 2:53 PM, Zhu Yanjun wrote: >>>> External email: Use caution opening links or attachments >>>> >>>> >>>> 在 2024/9/4 16:27, Edward Srouji 写道: >>>>> >>>>> On 9/4/2024 9:02 AM, Zhu Yanjun wrote: >>>>>> External email: Use caution opening links or attachments >>>>>> >>>>>> >>>>>> 在 2024/9/3 19:37, Leon Romanovsky 写道: >>>>>>> From: Leon Romanovsky <leonro@...dia.com> >>>>>>> >>>>>>> Hi, >>>>>>> >>>>>>> This series from Edward introduces mlx5 data direct placement (DDP) >>>>>>> feature. >>>>>>> >>>>>>> This feature allows WRs on the receiver side of the QP to be >>>>>>> consumed >>>>>>> out of order, permitting the sender side to transmit messages >>>>>>> without >>>>>>> guaranteeing arrival order on the receiver side. >>>>>>> >>>>>>> When enabled, the completion ordering of WRs remains in-order, >>>>>>> regardless of the Receive WRs consumption order. >>>>>>> >>>>>>> RDMA Read and RDMA Atomic operations on the responder side >>>>>>> continue to >>>>>>> be executed in-order, while the ordering of data placement for RDMA >>>>>>> Write and Send operations is not guaranteed. >>>>>> >>>>>> It is an interesting feature. If I got this feature correctly, this >>>>>> feature permits the user consumes the data out of order when RDMA >>>>>> Write >>>>>> and Send operations. But its completiong ordering is still in order. >>>>>> >>>>> Correct. >>>>>> Any scenario that this feature can be applied and what benefits >>>>>> will be >>>>>> got from this feature? >>>>>> >>>>>> I am just curious about this. Normally the users will consume the >>>>>> data >>>>>> in order. In what scenario, the user will consume the data out of >>>>>> order? >>>>>> >>>>> One of the main benefits of this feature is achieving higher >>>>> bandwidth >>>>> (BW) by allowing >>>>> responders to receive packets out of order (OOO). >>>>> >>>>> For example, this can be utilized in devices that support multi-plane >>>>> functionality, >>>>> as introduced in the "Multi-plane support for mlx5" series [1]. When >>>>> mlx5 multi-plane >>>>> is supported, a single logical mlx5 port aggregates multiple physical >>>>> plane ports. >>>>> In this scenario, the requester can "spray" packets across the >>>>> multiple physical >>>>> plane ports without guaranteeing packet order, either on the wire or >>>>> on the receiver >>>>> (responder) side. >>>>> >>>>> With this approach, no barriers or fences are required to ensure >>>>> in-order packet >>>>> reception, which optimizes the data path for performance. This can >>>>> result in better >>>>> BW, theoretically achieving line-rate performance equivalent to the >>>>> sum of >>>>> the maximum BW of all physical plane ports, with only one QP. >>>> >>>> Thanks a lot for your quick reply. Without ensuring in-order packet >>>> reception, this does optimize the data path for performance. >>>> >>>> I agree with you. >>>> >>>> But how does the receiver get the correct packets from the >>>> out-of-order >>>> packets efficiently? >>>> >>>> The method is implemented in Software or Hardware? >>> >>> >>> The packets have new field that is used by the HW to understand the >>> correct message order (similar to PSN). >>> >>> Once the packets arrive OOO to the receiver side, the data is scattered >>> directly (hence the DDP - "Direct Data Placement" name) by the HW. >>> >>> So the efficiency is achieved by the HW, as it also saves the required >>> context and metadata so it can deliver the correct completion to the >>> user (in-order) once we have some WQEs that can be considered an >>> "in-order window" and be delivered to the user. >>> >>> The SW/Applications may receive OOO WR_IDs though (because the first >>> CQE >>> may have consumed Recv WQE of any index on the receiver side), and it's >>> their responsibility to handle it from this point, if it's required. >> >> Got it. It seems that all the functionalities are implemented in HW. The >> SW only receives OOO WR_IDs. Thanks a lot. Perhaps it is helpful to RDMA >> LAG devices. It should enhance the performance^_^ >> >> BTW, do you have any performance data with this feature? > > Not yet. We tested it functionality wise for now. > > But we should be able to measure its performance soon :). Thanks a lot. It is an interesting feature. If performance reports, please share them with us. IMO, perhaps this feature can be used in random read/write devices, for example, hard disk? Just my idea. Not sure if you have applied this feature with hard disk or not. Best Regards, Zhu Yanjun > > >> >> Best Regards, >> Zhu Yanjun >> >>> >>>> >>>> I am just interested in this feature and want to know more about this. >>>> >>>> Thanks, >>>> >>>> Zhu Yanjun >>>> >>>>> >>>>> [1] >>>>> https://lore.kernel.org/lkml/cover.1718553901.git.leon@kernel.org/ >>>>>> Thanks, >>>>>> Zhu Yanjun >>>>>> >>>>>>> >>>>>>> Thanks >>>>>>> >>>>>>> Edward Srouji (2): >>>>>>> net/mlx5: Introduce data placement ordering bits >>>>>>> RDMA/mlx5: Support OOO RX WQE consumption >>>>>>> >>>>>>> drivers/infiniband/hw/mlx5/main.c | 8 +++++ >>>>>>> drivers/infiniband/hw/mlx5/mlx5_ib.h | 1 + >>>>>>> drivers/infiniband/hw/mlx5/qp.c | 51 >>>>>>> +++++++++++++++++++++++++--- >>>>>>> include/linux/mlx5/mlx5_ifc.h | 24 +++++++++---- >>>>>>> include/uapi/rdma/mlx5-abi.h | 5 +++ >>>>>>> 5 files changed, 78 insertions(+), 11 deletions(-) >>>>>>> >>>>>> >>>> -- >>>> Best Regards, >>>> Yanjun.Zhu >>>> >> -- Best Regards, Yanjun.Zhu
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