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

[Leon Romanovsky <leon@kernel.org>]

On Wed, Jan 05, 2022 at 08:42:03AM +0000, yanjun.zhu@linux.dev wrote:
> 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.

I'm asking if you use qp->src_port between this line and rxe_modify_qp?

Thanks

> 
> 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