Re: [PATCH 5/5] RDMA/rxe: Remove the redundant randomization for UDP source port

[yanjun.zhu@linux.dev]

January 5, 2022 3:49 PM, "Leon Romanovsky" <leon@kernel.org> wrote:

> On Wed, Jan 05, 2022 at 05:12:37PM -0500, yanjun.zhu@linux.dev wrote:
> 
>> From: Zhu Yanjun <yanjun.zhu@linux.dev>
>> 
>> Since the UDP source port is modified in rxe_modify_qp, the randomization
>> for UDP source port is redundant in this function. So remove it.
>> 
>> Signed-off-by: Zhu Yanjun <yanjun.zhu@linux.dev>
>> ---
>> drivers/infiniband/sw/rxe/rxe_qp.c | 10 ++--------
>> 1 file changed, 2 insertions(+), 8 deletions(-)
>> 
>> diff --git a/drivers/infiniband/sw/rxe/rxe_qp.c b/drivers/infiniband/sw/rxe/rxe_qp.c
>> index 54b8711321c1..84d6ffe7350a 100644
>> --- a/drivers/infiniband/sw/rxe/rxe_qp.c
>> +++ b/drivers/infiniband/sw/rxe/rxe_qp.c
>> @@ -210,15 +210,9 @@ static int rxe_qp_init_req(struct rxe_dev *rxe, struct rxe_qp *qp,
>> return err;
>> qp->sk->sk->sk_user_data = qp;
>> 
>> - /* pick a source UDP port number for this QP based on
>> - * the source QPN. this spreads traffic for different QPs
>> - * across different NIC RX queues (while using a single
>> - * flow for a given QP to maintain packet order).
>> - * the port number must be in the Dynamic Ports range
>> - * (0xc000 - 0xffff).
>> + /* Source UDP port number for this QP is modified in rxe_qp_modify.
>> */
> 
> This makes me wonder why do we set this src_port here?
> Are we using this field before modify QP?

The commit d3c04a3a6870 ("IB/rxe: vary the source udp port for receive scaling") sets this src_port here.

The advantage of setting src_port here is: before rxe_modify_qp, the src port is randomized, not 0xc000.
So after/before rxe_modify_qp, the src port is the same value.

If the src port is changed in rxe_modify_qp, before rxe_modify_qp, the src port is 0xc000, after rxe_modify_qp,
the src port is randomized, for example, src port is 0xF043.

So when the new method is adopted, I removed this.

Zhu Yanjun

> 
> Thanks
> 
>> - qp->src_port = RXE_ROCE_V2_SPORT +
>> - (hash_32_generic(qp_num(qp), 14) & 0x3fff);
>> + qp->src_port = RXE_ROCE_V2_SPORT;
>> qp->sq.max_wr = init->cap.max_send_wr;
>> 
>> /* These caps are limited by rxe_qp_chk_cap() done by the caller */
>> --
>> 2.27.0