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Message-ID: <aaf9263b-931e-4b1d-8aea-1218faec2802@linux.dev>
Date: Wed, 4 Sep 2024 19:53:12 +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 2024/9/4 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?
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
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