linux-kernel - Re: [PATCH] RDMA/mlx4: Spread completion vectors for proxy CQs

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Date:   Tue, 19 Feb 2019 09:58:24 -0500
From:   Chuck Lever <chuck.lever@...cle.com>
To:     Håkon Bugge <haakon.bugge@...cle.com>
Cc:     Yishai Hadas <yishaih@...lanox.com>,
        Doug Ledford <dledford@...hat.com>,
        Jason Gunthorpe <jgg@...pe.ca>, jackm@....mellanox.co.il,
        majd@...lanox.com, linux-rdma@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] RDMA/mlx4: Spread completion vectors for proxy CQs

Hey Håkon-

> On Feb 18, 2019, at 1:33 PM, Håkon Bugge <haakon.bugge@...cle.com> wrote:
> 
> MAD packet sending/receiving is not properly virtualized in
> CX-3. Hence, these are proxied through the PF driver. The proxying
> uses UD QPs. The associated CQs are created with completion vector
> zero.
> 
> This leads to great imbalance in CPU processing, in particular during
> heavy RDMA CM traffic.
> 
> Solved by selecting the completion vector on a round-robin base.

I've got a similar patch for NFS and NFSD. I'm wondering if this
should be turned into a core helper, simple as it is. Perhaps
it would be beneficial if all participating ULPs used the same
global counter?


> The imbalance can be demonstrated in a bare-metal environment, where
> two nodes have instantiated 8 VFs each. This using dual ported HCAs,
> so we have 16 vPorts per physical server.
> 
> 64 processes are associated with each vPort and creates and destroys
> one QP for each of the remote 64 processes. That is, 1024 QPs per
> vPort, all in all 16K QPs. The QPs are created/destroyed using the
> CM.
> 
> Before this commit, we have (excluding all completion IRQs with zero
> interrupts):
> 
> 396: mlx4-1@...0:94:00.0 199126
> 397: mlx4-2@...0:94:00.0 1
> 
> With this commit:
> 
> 396: mlx4-1@...0:94:00.0 12568
> 397: mlx4-2@...0:94:00.0 50772
> 398: mlx4-3@...0:94:00.0 10063
> 399: mlx4-4@...0:94:00.0 50753
> 400: mlx4-5@...0:94:00.0 6127
> 401: mlx4-6@...0:94:00.0 6114
> []
> 414: mlx4-19@...0:94:00.0 6122
> 415: mlx4-20@...0:94:00.0 6117
> 
> The added pr_info shows:
> 
> create_pv_resources: slave:0 port:1, vector:0, num_comp_vectors:62
> create_pv_resources: slave:0 port:1, vector:1, num_comp_vectors:62
> create_pv_resources: slave:0 port:2, vector:2, num_comp_vectors:62
> create_pv_resources: slave:0 port:2, vector:3, num_comp_vectors:62
> create_pv_resources: slave:1 port:1, vector:4, num_comp_vectors:62
> create_pv_resources: slave:1 port:2, vector:5, num_comp_vectors:62
> []
> create_pv_resources: slave:8 port:2, vector:18, num_comp_vectors:62
> create_pv_resources: slave:8 port:1, vector:19, num_comp_vectors:62
> 
> Signed-off-by: Håkon Bugge <haakon.bugge@...cle.com>
> ---
> drivers/infiniband/hw/mlx4/mad.c | 4 ++++
> 1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/infiniband/hw/mlx4/mad.c b/drivers/infiniband/hw/mlx4/mad.c
> index 936ee1314bcd..300839e7f519 100644
> --- a/drivers/infiniband/hw/mlx4/mad.c
> +++ b/drivers/infiniband/hw/mlx4/mad.c
> @@ -1973,6 +1973,7 @@ static int create_pv_resources(struct ib_device *ibdev, int slave, int port,
> {
> 	int ret, cq_size;
> 	struct ib_cq_init_attr cq_attr = {};
> +	static atomic_t comp_vect = ATOMIC_INIT(-1);
> 
> 	if (ctx->state != DEMUX_PV_STATE_DOWN)
> 		return -EEXIST;
> @@ -2002,6 +2003,9 @@ static int create_pv_resources(struct ib_device *ibdev, int slave, int port,
> 		cq_size *= 2;
> 
> 	cq_attr.cqe = cq_size;
> +	cq_attr.comp_vector = atomic_inc_return(&comp_vect) % ibdev->num_comp_vectors;
> +	pr_info("slave:%d port:%d, vector:%d, num_comp_vectors:%d\n",
> +		slave, port, cq_attr.comp_vector, ibdev->num_comp_vectors);
> 	ctx->cq = ib_create_cq(ctx->ib_dev, mlx4_ib_tunnel_comp_handler,
> 			       NULL, ctx, &cq_attr);
> 	if (IS_ERR(ctx->cq)) {
> -- 
> 2.20.1
> 

--
Chuck Lever