Linux Soft-RoCE implementation （zz）

Linux Soft-RoCE implementation

首页分类标签留言关于订阅2017-11-08 | 分类 Network  | 标签 RDMA  RoCE  Linux-RDMA

内核在4.9实现的Soft-RoCE实现了RoCEv2.

队列初始化

libRXE (user space library)

ibv_create_qp
|--- rxe_create_qp
    |--- ibv_cmd_create_qp

• ibv_create_qp

LATEST_SYMVER_FUNC(ibv_create_qp, 1_1, "IBVERBS_1.1",
		   struct ibv_qp *,
		   struct ibv_pd *pd,
		   struct ibv_qp_init_attr *qp_init_attr)
{
	struct ibv_qp *qp = pd->context->ops.create_qp(pd, qp_init_attr); ///rxe_ctx_ops
///..
}

• rxe_create_qp

static struct ibv_qp *rxe_create_qp(struct ibv_pd *pd,
				    struct ibv_qp_init_attr *attr)
{
	struct ibv_create_qp cmd;
	struct rxe_create_qp_resp resp;
	struct rxe_qp *qp;
	int ret;
////..
	ret = ibv_cmd_create_qp(pd, &qp->ibv_qp, attr, &cmd, sizeof cmd,
				&resp.ibv_resp, sizeof resp); /// ibv_create_qp CMD, to kernel
///...
	qp->sq.max_sge = attr->cap.max_send_sge;
	qp->sq.max_inline = attr->cap.max_inline_data;
	qp->sq.queue = mmap(NULL, resp.sq_mi.size, PROT_READ | PROT_WRITE,
			    MAP_SHARED,
			    pd->context->cmd_fd, resp.sq_mi.offset); ///mmap，参考rxe_mmap

ibv_context->cmd_fd指向对应的ibv_device，由ibv_open_device返回。

ibv_cmd_create_qp会通过ibv_context->cmd_fd给内核发送IB_USER_VERBS_CMD_CREATE_QP命令，参考libiverbs@ibv_cmd_create_qp.

对应的内核write函数为ib_uverbs_write:

///drivers/infiniband/core/uverbs_main.c
static const struct file_operations uverbs_fops = {
	.owner	 = THIS_MODULE,
	.write	 = ib_uverbs_write,
	.open	 = ib_uverbs_open,
	.release = ib_uverbs_close,
	.llseek	 = no_llseek,
};

• ibv_open_device

///libibverbs/device.c
LATEST_SYMVER_FUNC(ibv_open_device, 1_1, "IBVERBS_1.1",
		   struct ibv_context *,
		   struct ibv_device *device)
{
	struct verbs_device *verbs_device = verbs_get_device(device);
	char *devpath;
	int cmd_fd, ret;
	struct ibv_context *context;
	struct verbs_context *context_ex;

	if (asprintf(&devpath, "/dev/infiniband/%s", device->dev_name) < 0)
		return NULL;

	/*
	 * We'll only be doing writes, but we need O_RDWR in case the
	 * provider needs to mmap() the file.
	 */
	cmd_fd = open(devpath, O_RDWR | O_CLOEXEC); /// /dev/infiniband/uverbs0
	free(devpath);

	if (cmd_fd < 0)
		return NULL;

	if (!verbs_device->ops->init_context) {
		context = verbs_device->ops->alloc_context(device, cmd_fd); ///rxe_alloc_context, rxe_dev_ops
		if (!context)
			goto err;
	}
///...
	context->device = device;
	context->cmd_fd = cmd_fd;
	pthread_mutex_init(&context->mutex, NULL);

	ibverbs_device_hold(device);

	return context;
///...
}

kernel (rdma_rxe module)

• ib_uverbs_create_qp

IB_USER_VERBS_CMD_CREATE_QP的处理函数为函数ib_uverbs_create_qp.

ib_uverbs_write
|--- ib_uverbs_create_qp
     |--- create_qp
	      |--- ib_device->create_qp
		       |--- rxe_create_qp

create_qp调用ib_device->create_qp,对于RXE， 为函数rxe_create_qp， 参考rxe_register_device.

• rxe_create_qp

rxe_create_qp
|--- rxe_qp_from_init
     |--- rxe_qp_init_req

rxe_qp_from_init完成发送队列和接收队列的初始化。

• rxe_qp_init_req

rxe_qp_init_req主要做以下一些事情：

创建对应的UDP socket

调用rxe_queue_init完成发送队列的初始化.

初始化对应的tasklet

• rxe_queue_init

rxe_queue_init给队列分配内存空间：

struct rxe_queue *rxe_queue_init(struct rxe_dev *rxe,
				 int *num_elem,
				 unsigned int elem_size)
{
	struct rxe_queue *q;
	size_t buf_size;
	unsigned int num_slots;
///...
	buf_size = sizeof(struct rxe_queue_buf) + num_slots * elem_size;

	q->buf = vmalloc_user(buf_size);
///...
}

rxe_queue->buf指向的内存缓冲区，由rxe_mmap映射到用户空间，队列的element对应数据结构struct rxe_send_wqe.

libiverbs API调用ibv_post_send时，会将对应的struct rxe_send_wqe加入到该队列，参考rdma-core@post_one_send.

• rxe_mmap

/**
 * rxe_mmap - create a new mmap region
 * @context: the IB user context of the process making the mmap() call
 * @vma: the VMA to be initialized
 * Return zero if the mmap is OK. Otherwise, return an errno.
 */
int rxe_mmap(struct ib_ucontext *context, struct vm_area_struct *vma)
{
	struct rxe_dev *rxe = to_rdev(context->device);
	unsigned long offset = vma->vm_pgoff << PAGE_SHIFT;
	unsigned long size = vma->vm_end - vma->vm_start;
	struct rxe_mmap_info *ip, *pp;
///...
found_it:
	list_del_init(&ip->pending_mmaps);
	spin_unlock_bh(&rxe->pending_lock);

	ret = remap_vmalloc_range(vma, ip->obj, 0);
	if (ret) {
		pr_err("rxe: err %d from remap_vmalloc_range\n", ret);
		goto done;
	}

	vma->vm_ops = &rxe_vm_ops;
	vma->vm_private_data = ip;
	rxe_vma_open(vma);
///...
}

发送数据

libRXE

rxe_post_send会将struct ibv_send_wr转成struct rxe_send_wqe，并加入到发送队列rxe_qp->rq，然后通过cmd_fd给RXE内核模块发送IB_USER_VERBS_CMD_POST_SEND命令：

///providers/rxe/rxe.c
/* this API does not make a distinction between
   restartable and non-restartable errors */
static int rxe_post_send(struct ibv_qp *ibqp,
			 struct ibv_send_wr *wr_list,
			 struct ibv_send_wr **bad_wr)
{
	int rc = 0;
	int err;
	struct rxe_qp *qp = to_rqp(ibqp);/// ibv_qp -> rxe_qp
	struct rxe_wq *sq = &qp->sq;

	if (!bad_wr)
		return EINVAL;

	*bad_wr = NULL;

	if (!sq || !wr_list || !sq->queue)
	 	return EINVAL;

	pthread_spin_lock(&sq->lock);

	while (wr_list) {
		rc = post_one_send(qp, sq, wr_list); /// ibv_send_wr -> rxe_send_wqe, enqueue
		if (rc) {
			*bad_wr = wr_list;
			break;
		}

		wr_list = wr_list->next;
	}

	pthread_spin_unlock(&sq->lock);

	err =  post_send_db(ibqp); /// IB_USER_VERBS_CMD_POST_SEND cmd
	return err ? err : rc;
}

kernel

处理的IB_USER_VERBS_CMD_POST_SEND的函数为ib_uverbs_post_send:

ib_uverbs_post_send -> ib_device->post_send -> rxe_post_send -> rxe_requester -> ip_local_out。

• rxe_post_send

static int rxe_post_send(struct ib_qp *ibqp, struct ib_send_wr *wr,
			 struct ib_send_wr **bad_wr)
{
	int err = 0;
	struct rxe_qp *qp = to_rqp(ibqp); ///ib_qp -> rxe_qp
///...
	/*
	 * Must sched in case of GSI QP because ib_send_mad() hold irq lock,
	 * and the requester call ip_local_out_sk() that takes spin_lock_bh.
	 */
	must_sched = (qp_type(qp) == IB_QPT_GSI) ||
			(queue_count(qp->sq.queue) > 1);

	rxe_run_task(&qp->req.task, must_sched); /// to rxe_requester

	return err;
}

• rxe_requester

rxe_requester从rxe_qp队列取出rxe_send_wqe，生成对应的skb_buff，然后下发给对应的rxe_dev设备：

///sw/rxe/rxe_req.c
int rxe_requester(void *arg)
{
	struct rxe_qp *qp = (struct rxe_qp *)arg;
	struct rxe_pkt_info pkt;
	struct sk_buff *skb;
	struct rxe_send_wqe *wqe;
///...
	wqe = req_next_wqe(qp); /// get rxe_send_wqe
///...
	/// rxe_send_wqe -> skb
	skb = init_req_packet(qp, wqe, opcode, payload, &pkt);
///...
	ret = rxe_xmit_packet(to_rdev(qp->ibqp.device), qp, &pkt, skb);
///...
}

static inline int rxe_xmit_packet(struct rxe_dev *rxe, struct rxe_qp *qp,
				  struct rxe_pkt_info *pkt, struct sk_buff *skb)
{
///...
	if (pkt->mask & RXE_LOOPBACK_MASK) {
		memcpy(SKB_TO_PKT(skb), pkt, sizeof(*pkt));
		err = rxe->ifc_ops->loopback(skb);
	} else {
		err = rxe->ifc_ops->send(rxe, pkt, skb);/// ifc_ops->send, send
	}
///...
}

ifc_ops->send最后会调用ip_local_out，从对应的物理NIC发送出去。

Refs

• SOFT-RoCE RDMA TRANSPORT IN A SOFTWARE IMPLEMENTATION
• THE LINUX SOFTROCE DRIVER