Subject: Re: [MAINLINE 2/2] rds: ib: Add Dynamic Interrupt Moderation to CQs

From: Zhu Yanjun <[email-masked]>
Date: Sat, 21 Sep 2024 21:43:12 +0800

在 2024/9/18 16:35, Håkon Bugge 写道:
> With the support from ib_core to use Dynamic Interrupt Moderation
> (DIM) from legacy ULPs, which uses ib_create_cq(), we enable that
> feature for the receive and send CQs in RDS.
> 
> A set of rds-stress runs have been done. bcopy read + write for
> payload 8448 and 16640 bytes and ack/req of 256 bytes. Number of QPs
> varies from 8 to 128, number of threads (i.e. rds-stress processes)
> from one to 16 and a depth of four. A limit has been applied such that
> the number of processes times the number of QPs never exceeds 128. All
> in all, 61 rds-stress runs.
> 
> For brevity, only the rows showing a +/- 3% deviation or larger from
> base is listed. The geometric mean of the ratios (IOPS_test /
> IOPS_base) is calculated for all 61 runs, and that gives the best
> possible "average" impact of the commits.
> 
> In the following, "base" is v6.11-rc7. "test" is the same
> kernel with the following two commits:
> 
>         * rds: ib: Add Dynamic Interrupt Moderation to CQs (this commit)
>         * RDMA/core: Enable legacy ULPs to use RDMA DIM
> 
> This is executed between two X8-2 with CX-5 using fw 16.35.3502. These
> BM systems were instantiated with one VF, which were used for the
> test:
> 
>                                   base     test
>     ACK    REQ  QPS  THR  DEP     IOPS     IOPS  Percent
>     256   8448    8    1    4   634463   658162      3.7
>     256   8448    8    2    4   862648   997358     15.6
>     256   8448    8    4    4   950458  1113991     17.2
>     256   8448    8    8    4   932120  1127024     20.9
>     256   8448    8   16    4   944977  1133885     20.0
>    8448    256    8    2    4   858663   975563     13.6
>    8448    256    8    4    4   934884  1098854     17.5
>    8448    256    8    8    4   928247  1116015     20.2
>    8448    256    8   16    4   938864  1123455     19.7
>     256   8448   64    1    4   965985   918445     -4.9
>    8448    256   64    1    4   963280   918239     -4.7
>     256  16640    8    2    4   544670   582330      6.9
>     256  16640    8    4    4   554873   597553      7.7
>     256  16640    8    8    4   551799   597479      8.3
>     256  16640    8   16    4   553041   597898      8.1
>   16640    256    8    2    4   544644   578331      6.2
>   16640    256    8    4    4   553944   594627      7.3
>   16640    256    8    8    4   551388   594737      7.9
>   16640    256    8   16    4   552986   596581      7.9
> Geometric mean of ratios: 1.03
> 
> Signed-off-by: Håkon Bugge <[email-masked]>
> ---
>   net/rds/ib_cm.c | 10 ++++++++++
>   1 file changed, 10 insertions(+)
> 
> diff --git a/net/rds/ib_cm.c b/net/rds/ib_cm.c
> index 26b069e1999df..79603d86b6c02 100644
> --- a/net/rds/ib_cm.c
> +++ b/net/rds/ib_cm.c
> @@ -259,6 +259,7 @@ static void rds_ib_cq_comp_handler_recv(struct ib_cq *cq, void *context)
>   static void poll_scq(struct rds_ib_connection *ic, struct ib_cq *cq,
>   		     struct ib_wc *wcs)
>   {
> +	int ncompleted = 0;
>   	int nr, i;
>   	struct ib_wc *wc;
>   
> @@ -276,7 +277,10 @@ static void poll_scq(struct rds_ib_connection *ic, struct ib_cq *cq,
>   				rds_ib_mr_cqe_handler(ic, wc);
>   
>   		}
> +		ncompleted += nr;
>   	}
> +	if (cq->dim)
> +		rdma_dim(cq->dim, ncompleted);
>   }
>   
>   static void rds_ib_tasklet_fn_send(unsigned long data)
> @@ -304,6 +308,7 @@ static void poll_rcq(struct rds_ib_connection *ic, struct ib_cq *cq,
>   		     struct ib_wc *wcs,
>   		     struct rds_ib_ack_state *ack_state)
>   {
> +	int ncompleted = 0;
>   	int nr, i;
>   	struct ib_wc *wc;
>   
> @@ -316,7 +321,10 @@ static void poll_rcq(struct rds_ib_connection *ic, struct ib_cq *cq,
>   
>   			rds_ib_recv_cqe_handler(ic, wc, ack_state);
>   		}
> +		ncompleted += nr;
>   	}
> +	if (cq->dim)
> +		rdma_dim(cq->dim, ncompleted);
>   }
>   
>   static void rds_ib_tasklet_fn_recv(unsigned long data)
> @@ -542,6 +550,7 @@ static int rds_ib_setup_qp(struct rds_connection *conn)
>   	ic->i_scq_vector = ibdev_get_unused_vector(rds_ibdev);
>   	cq_attr.cqe = ic->i_send_ring.w_nr + fr_queue_space + 1;
>   	cq_attr.comp_vector = ic->i_scq_vector;
> +	cq_attr.flags |= IB_CQ_MODERATE;

cq_attr.flags is added IB_CQ_MODERATE here.

>   	ic->i_send_cq = ib_create_cq(dev, rds_ib_cq_comp_handler_send,
>   				     rds_ib_cq_event_handler, conn,
>   				     &cq_attr);
> @@ -556,6 +565,7 @@ static int rds_ib_setup_qp(struct rds_connection *conn)
>   	ic->i_rcq_vector = ibdev_get_unused_vector(rds_ibdev);
>   	cq_attr.cqe = ic->i_recv_ring.w_nr;
>   	cq_attr.comp_vector = ic->i_rcq_vector;
> +	cq_attr.flags |= IB_CQ_MODERATE;

Why is cq_attr.flags add IB_CQ_MODERATE again?
Is this cq_attr.flags changed before this line?

Zhu Yanjun

>   	ic->i_recv_cq = ib_create_cq(dev, rds_ib_cq_comp_handler_recv,
>   				     rds_ib_cq_event_handler, conn,
>   				     &cq_attr);