RE: [RFC PATCH rdma-next 00/10] RDMA/rxe: Add RDMA FLUSH operation

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1)
> rdma_post_flush(struct rdma_cm_id *id, void *context, struct ibv_sge *sgl,
>		int nsge, int flags, uint32_t type, uint32_t level,
>		uint64_t remote_addr, uint32_t rkey)
Shall we not use struct ibv_sge *sgl in this API call but explicitly use flush length (DMALen) argument?
It will be similar to other rdma_post_XXX API calls where ibv_sge is not used at all.
Ibv_sge is used only in rdma_post_XXXv API calls.

2)
>struct ibv_send_wr {
>...
> 	union {
>		struct {
>			uint64_t	remote_addr;
>			uint32_t	rkey;
>			uint32_t	type;
>			uint32_t	level;
>		} flush;

Shall we extend this structure with 
uint32_t length
and abandon using *sg_list as it is related in RDMA verbs to local memory access only:

Ibv_post_send.3:
struct ibv_sge         *sg_list;                /* Pointer to the s/g array */
int                     num_sge;                /* Size of the s/g array */

In the case of flush, there is no local context at all.

Thanks
Tomasz

> -----Original Message-----
> From: Li Zhijian <lizhijian@xxxxxxxxxxxxxx>
> Sent: Tuesday, December 28, 2021 9:07 AM
> To: linux-rdma@xxxxxxxxxxxxxxx; zyjzyj2000@xxxxxxxxx; jgg@xxxxxxxx;
> aharonl@xxxxxxxxxx; leon@xxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx; mbloch@xxxxxxxxxx;
> liweihang@xxxxxxxxxx; liangwenpeng@xxxxxxxxxx;
> yangx.jy@xxxxxxxxxxxxxx; rpearsonhpe@xxxxxxxxx; y-goto@xxxxxxxxxxx; Li
> Zhijian <lizhijian@xxxxxxxxxxxxxx>
> Subject: [RFC PATCH rdma-next 00/10] RDMA/rxe: Add RDMA FLUSH
> operation
> 
> Hey folks,
> 
> These patches are going to implement a *NEW* RDMA opcode "RDMA
> FLUSH".
> In IB SPEC 1.5[1][2], 2 new opcodes, ATOMIC WRITE and RDMA FLUSH were
> added in the MEMORY PLACEMENT EXTENSIONS section.
> 
> FLUSH is used by the requesting node to achieve guarantees on the data
> placement within the memory subsystem of preceding accesses to a single
> memory region, such as those performed by RDMA WRITE, Atomics and
> ATOMIC WRITE requests.
> 
> The operation indicates the virtual address space of a destination node and
> where the guarantees should apply. This range must be contiguous in the
> virtual space of the memory key but it is not necessarily a contiguous range
> of physical memory.
> 
> FLUSH packets carry FLUSH extended transport header (see below) to
> specify the placement type and the selectivity level of the operation and
> RDMA extended header (RETH, see base document RETH definition) to
> specify the R_Key VA and Length associated with this request following the
> BTH in RC, RDETH in RD and XRCETH in XRC.
> 
> RC FLUSH:
> +----+------+------+
> |BTH | FETH | RETH |
> +----+------+------+
> 
> RD FLUSH:
> +----+------+------+------+
> |BTH | RDETH| FETH | RETH |
> +----+------+------+------+
> 
> XRC FLUSH:
> +----+-------+------+------+
> |BTH | XRCETH| FETH | RETH |
> +----+-------+------+------+
> 
> Currently, we introduce RC and RD services only, since XRC has not been
> implemented by rxe yet.
> NOTE: only RC service is tested now, and since other HCAs have not
> added/implemented FLUSH yet, we can only test FLUSH operation in both
> SoftRoCE/rxe devices.
> 
> The corresponding rdma-core and FLUSH example are available on:
> https://github.com/zhijianli88/rdma-core/tree/rfc
> 
> Below list some details about FLUSH transport packet:
> 
> A FLUSH message is built upon FLUSH request packet and is responded
> successfully by RDMA READ response of zero size.
> 
> oA19-2: FLUSH shall be single packet message and shall have no payload.
> 
> oA19-2: FLUSH shall be single packet message and shall have no payload.
> oA19-5: FLUSH BTH shall hold the Opcode = 0x1C
> 
> FLUSH Extended Transport Header(FETH)
> +-----+-----------+------------------------+----------------------+
> |Bits |   31-6    |          5-4           |        3-0           |
> +-----+-----------+------------------------+----------------------+
> |     | Reserved  | Selectivity Level(SEL) | Placement Type(PLT)  |
> +-----+-----------+------------------------+----------------------+
> 
> Selectivity Level (SEL) – defines the memory region scope the FLUSH should
> apply on. Values are as follows:
> • b’00 - Memory Region Range: FLUSH applies for all preceding memory
>          updates to the RETH range on this QP. All RETH fields shall be
>          valid in this selectivity mode. RETH:DMALen field shall be
>          between zero and (2 31 -1) bytes (inclusive).
> • b’01 - Memory Region: FLUSH applies for all preceding memory up-
>          dates to RETH.R_key on this QP. RETH:DMALen and RETH:VA
>          shall be ignored in this mode.
> • b'10 - Reserved.
> • b'11 - Reserved.
> 
> Placement Type (PLT) – Defines the memory placement guarantee of this
> FLUSH. Multiple bits may be set in this field. Values are as follows:
> • Bit 0 if set to '1' indicated that the FLUSH should guarantee Global
>   Visibility.
> • Bit 1 if set to '1' indicated that the FLUSH should guarantee
>   Persistence.
> • Bits 3:2 are reserved
> 
> [1]: https://www.infinibandta.org/ibta-specification/ # login required
> [2]: https://www.infinibandta.org/wp-content/uploads/2021/08/IBTA-
> Overview-of-IBTA-Volume-1-Release-1.5-and-MPE-2021-08-17-Secure.pptx
> 
> CC: Jason Gunthorpe <jgg@xxxxxxxx>
> CC: Zhu Yanjun <zyjzyj2000@xxxxxxxxx
> CC: Leon Romanovsky <leon@xxxxxxxxxx>
> CC: Bob Pearson <rpearsonhpe@xxxxxxxxx>
> CC: Weihang Li <liweihang@xxxxxxxxxx>
> CC: Mark Bloch <mbloch@xxxxxxxxxx>
> CC: Wenpeng Liang <liangwenpeng@xxxxxxxxxx>
> CC: Aharon Landau <aharonl@xxxxxxxxxx>
> CC: linux-rdma@xxxxxxxxxxxxxxx
> CC: linux-kernel@xxxxxxxxxxxxxxx
> 
> Li Zhijian (10):
>   RDMA: mr: Introduce is_pmem
>   RDMA: Allow registering MR with flush access flags
>   RDMA/rxe: Allow registering FLUSH flags for supported device only
>   RDMA/rxe: Enable IB_DEVICE_RDMA_FLUSH for rxe device
>   RDMA/rxe: Allow registering persistent flag for pmem MR only
>   RDMA/rxe: Implement RC RDMA FLUSH service in requester side
>   RDMA/rxe: Set BTH's SE to zero for FLUSH packet
>   RDMA/rxe: Implement flush execution in responder side
>   RDMA/rxe: Implement flush completion
>   RDMA/rxe: Add RD FLUSH service support
> 
>  drivers/infiniband/core/uverbs_cmd.c    |  16 +++
>  drivers/infiniband/sw/rxe/rxe_comp.c    |   4 +-
>  drivers/infiniband/sw/rxe/rxe_hdr.h     |  52 ++++++++++
>  drivers/infiniband/sw/rxe/rxe_loc.h     |   2 +
>  drivers/infiniband/sw/rxe/rxe_mr.c      |  63 +++++++++++-
>  drivers/infiniband/sw/rxe/rxe_opcode.c  |  33 ++++++
>  drivers/infiniband/sw/rxe/rxe_opcode.h  |   3 +
>  drivers/infiniband/sw/rxe/rxe_param.h   |   3 +-
>  drivers/infiniband/sw/rxe/rxe_req.c     |  14 ++-
>  drivers/infiniband/sw/rxe/rxe_resp.c    | 131 +++++++++++++++++++++++-
>  include/rdma/ib_pack.h                  |   3 +
>  include/rdma/ib_verbs.h                 |  22 +++-
>  include/uapi/rdma/ib_user_ioctl_verbs.h |   2 +
>  include/uapi/rdma/ib_user_verbs.h       |  18 ++++
>  include/uapi/rdma/rdma_user_rxe.h       |   6 ++
>  15 files changed, 362 insertions(+), 10 deletions(-)
> 
> --
> 2.31.1
> 
> 

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