RDMA/core: Provide RDMA DIM support for ULPs

Added the interface in the infiniband driver that applies the rdma_dim
adaptive moderation. There is now a special function for allocating an
ib_cq that uses rdma_dim.

Performance improvement (ConnectX-5 100GbE, x86) running FIO benchmark over
NVMf between two equal end-hosts with 56 cores across a Mellanox switch
using null_blk device:

READS without DIM:
blk size | BW | IOPS | 99th percentile latency | 99.99th latency
512B | 3.8GiB/s | 7.7M | 1401 usec | 2442 usec
4k | 7.0GiB/s | 1.8M | 4817 usec | 6587 usec
64k | 10.7GiB/s| 175k | 9896 usec | 10028 usec

IO WRITES without DIM:
blk size | BW | IOPS | 99th percentile latency | 99.99th latency
512B | 3.6GiB/s | 7.5M | 1434 usec | 2474 usec
4k | 6.3GiB/s | 1.6M | 938 usec | 1221 usec
64k | 10.7GiB/s| 175k | 8979 usec | 12780 usec

IO READS with DIM:
blk size | BW | IOPS | 99th percentile latency | 99.99th latency
512B | 4GiB/s | 8.2M | 816 usec | 889 usec
4k | 10.1GiB/s| 2.65M| 3359 usec | 5080 usec
64k | 10.7GiB/s| 175k | 9896 usec | 10028 usec

IO WRITES with DIM:
blk size | BW | IOPS | 99th percentile latency | 99.99th latency
512B | 3.9GiB/s | 8.1M | 799 usec | 922 usec
4k | 9.6GiB/s | 2.5M | 717 usec | 1004 usec
64k | 10.7GiB/s| 176k | 8586 usec | 12256 usec

The rdma_dim algorithm was designed to measure the effectiveness of
moderation on the flow in a general way and thus should be appropriate
for all RDMA storage protocols.

rdma_dim is configured to be the default option based on performance
improvement seen after extensive tests.

Signed-off-by: Yamin Friedman <[e-mail]>
Reviewed-by: Max Gurtovoy <[e-mail]>
Reviewed-by: Sagi Grimberg <[e-mail]>
Signed-off-by: Saeed Mahameed <[e-mail]>
Signed-off-by: Leon Romanovsky <[e-mail]>
Signed-off-by: Jason Gunthorpe <[e-mail]>

drivers/infiniband/core/cq.c

···
 #define IB_POLL_FLAGS \
 	(IB_CQ_NEXT_COMP | IB_CQ_REPORT_MISSED_EVENTS)
 
+static void ib_cq_rdma_dim_work(struct work_struct *w)
+{
+	struct dim *dim = container_of(w, struct dim, work);
+	struct ib_cq *cq = dim->priv;
+
+	u16 usec = rdma_dim_prof[dim->profile_ix].usec;
+	u16 comps = rdma_dim_prof[dim->profile_ix].comps;
+
+	dim->state = DIM_START_MEASURE;
+
+	cq->device->ops.modify_cq(cq, comps, usec);
+}
+
+static void rdma_dim_init(struct ib_cq *cq)
+{
+	struct dim *dim;
+
+	if (!cq->device->ops.modify_cq || !cq->device->use_cq_dim ||
+	    cq->poll_ctx == IB_POLL_DIRECT)
+		return;
+
+	dim = kzalloc(sizeof(struct dim), GFP_KERNEL);
+	if (!dim)
+		return;
+
+	dim->state = DIM_START_MEASURE;
+	dim->tune_state = DIM_GOING_RIGHT;
+	dim->profile_ix = RDMA_DIM_START_PROFILE;
+	dim->priv = cq;
+	cq->dim = dim;
+
+	INIT_WORK(&dim->work, ib_cq_rdma_dim_work);
+}
+
 static int __ib_process_cq(struct ib_cq *cq, int budget, struct ib_wc *wcs,
 			   int batch)
 {
···
 static int ib_poll_handler(struct irq_poll *iop, int budget)
 {
 	struct ib_cq *cq = container_of(iop, struct ib_cq, iop);
+	struct dim *dim = cq->dim;
 	int completed;
 
 	completed = __ib_process_cq(cq, budget, cq->wc, IB_POLL_BATCH);
···
 		if (ib_req_notify_cq(cq, IB_POLL_FLAGS) > 0)
 			irq_poll_sched(&cq->iop);
 	}
+
+	if (dim)
+		rdma_dim(dim, completed);
 
 	return completed;
 }
···
 	if (completed >= IB_POLL_BUDGET_WORKQUEUE ||
 	    ib_req_notify_cq(cq, IB_POLL_FLAGS) > 0)
 		queue_work(cq->comp_wq, &cq->work);
+	else if (cq->dim)
+		rdma_dim(cq->dim, completed);
 }
 
 static void ib_cq_completion_workqueue(struct ib_cq *cq, void *private)
···
 		goto out_free_wc;
 
 	rdma_restrack_kadd(&cq->res);
+
+	rdma_dim_init(cq);
 
 	switch (cq->poll_ctx) {
 	case IB_POLL_DIRECT:
···
 
 	rdma_restrack_del(&cq->res);
 	cq->device->ops.destroy_cq(cq, udata);
+	if (cq->dim)
+		cancel_work_sync(&cq->dim->work);
+	kfree(cq->dim);
 	kfree(cq->wc);
 	kfree(cq);
 }

include/rdma/ib_verbs.h

···
 #include <linux/cgroup_rdma.h>
 #include <linux/irqflags.h>
 #include <linux/preempt.h>
+#include <linux/dim.h>
 #include <uapi/rdma/ib_user_verbs.h>
 #include <rdma/rdma_counter.h>
 #include <rdma/restrack.h>
···
 		struct work_struct	work;
 	};
 	struct workqueue_struct *comp_wq;
+	struct dim *dim;
 	/*
 	 * Implementation details of the RDMA core, don't use in drivers:
 	 */
···
 	u16                          is_switch:1;
 	/* Indicates kernel verbs support, should not be used in drivers */
 	u16                          kverbs_provider:1;
+	/* CQ adaptive moderation (RDMA DIM) */
+	u16                          use_cq_dim:1;
 	u8                           node_type;
 	u8                           phys_port_cnt;
 	struct ib_device_attr        attrs;