Re: [PATCH v20 05/20] nvme-tcp: Add DDP offload control path

Sagi Grimberg
2023-11-28T10:31:24Z

On 11/22/23 15:48, Aurelien Aptel wrote:
> From: Boris Pismenny <borisp@nvidia.com>
>
> This commit introduces direct data placement offload to NVME
> TCP. There is a context per queue, which is established after the
> handshake using the sk_add/del NDOs.
>
> Additionally, a resynchronization routine is used to assist
> hardware recovery from TCP OOO, and continue the offload.
> Resynchronization operates as follows:
>
> 1. TCP OOO causes the NIC HW to stop the offload
>
> 2. NIC HW identifies a PDU header at some TCP sequence number,
> and asks NVMe-TCP to confirm it.
> This request is delivered from the NIC driver to NVMe-TCP by first
> finding the socket for the packet that triggered the request, and
> then finding the nvme_tcp_queue that is used by this routine.
> Finally, the request is recorded in the nvme_tcp_queue.
>
> 3. When NVMe-TCP observes the requested TCP sequence, it will compare
> it with the PDU header TCP sequence, and report the result to the
> NIC driver (resync), which will update the HW, and resume offload
> when all is successful.
>
> Some HW implementation such as ConnectX-7 assume linear CCID (0...N-1
> for queue of size N) where the linux nvme driver uses part of the 16
> bit CCID for generation counter. To address that, we use the existing
> quirk in the nvme layer when the HW driver advertises if the device is
> not supports the full 16 bit CCID range.
>
> Furthermore, we let the offloading driver advertise what is the max hw
> sectors/segments via ulp_ddp_limits.
>
> A follow-up patch introduces the data-path changes required for this
> offload.
>
> Socket operations need a netdev reference. This reference is
> dropped on NETDEV_GOING_DOWN events to allow the device to go down in
> a follow-up patch.
>
> Signed-off-by: Boris Pismenny <borisp@nvidia.com>
> Signed-off-by: Ben Ben-Ishay <benishay@nvidia.com>
> Signed-off-by: Or Gerlitz <ogerlitz@nvidia.com>
> Signed-off-by: Yoray Zack <yorayz@nvidia.com>
> Signed-off-by: Shai Malin <smalin@nvidia.com>
> Signed-off-by: Aurelien Aptel <aaptel@nvidia.com>
> Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
> ---
> drivers/nvme/host/tcp.c | 259 ++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 246 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/nvme/host/tcp.c b/drivers/nvme/host/tcp.c
> index 89661a9cf850..7ad6a4854fce 100644
> --- a/drivers/nvme/host/tcp.c
> +++ b/drivers/nvme/host/tcp.c
> @@ -21,6 +21,10 @@
> #include <net/busy_poll.h>
> #include <trace/events/sock.h>
>
> +#ifdef CONFIG_ULP_DDP
> +#include <net/ulp_ddp.h>
> +#endif
> +
> #include "nvme.h"
> #include "fabrics.h"
>
> @@ -46,6 +50,16 @@ MODULE_PARM_DESC(tls_handshake_timeout,
> "nvme TLS handshake timeout in seconds (default 10)");
> #endif
>
> +#ifdef CONFIG_ULP_DDP
> +/* NVMeTCP direct data placement and data digest offload will not
> + * happen if this parameter false (default), regardless of what the
> + * underlying netdev capabilities are.
> + */
> +static bool ddp_offload;
> +module_param(ddp_offload, bool, 0644);
> +MODULE_PARM_DESC(ddp_offload, "Enable or disable NVMeTCP direct data placement support");
> +#endif
> +
> #ifdef CONFIG_DEBUG_LOCK_ALLOC
> /* lockdep can detect a circular dependency of the form
> * sk_lock -> mmap_lock (page fault) -> fs locks -> sk_lock
> @@ -119,6 +133,7 @@ enum nvme_tcp_queue_flags {
> NVME_TCP_Q_ALLOCATED = 0,
> NVME_TCP_Q_LIVE = 1,
> NVME_TCP_Q_POLLING = 2,
> + NVME_TCP_Q_OFF_DDP = 3,
> };
>
> enum nvme_tcp_recv_state {
> @@ -146,6 +161,18 @@ struct nvme_tcp_queue {
> size_t ddgst_remaining;
> unsigned int nr_cqe;
>
> +#ifdef CONFIG_ULP_DDP
> + /*
> + * resync_tcp_seq is a speculative PDU header tcp seq number (with
> + * an additional flag in the lower 32 bits) that the HW send to
> + * the SW, for the SW to verify.
> + * - The 32 high bits store the seq number
> + * - The 32 low bits are used as a flag to know if a request
> + * is pending (ULP_DDP_RESYNC_PENDING).
> + */
> + atomic64_t resync_tcp_seq;
> +#endif
> +
> /* send state */
> struct nvme_tcp_request *request;
>
> @@ -188,6 +215,12 @@ struct nvme_tcp_ctrl {
> struct delayed_work connect_work;
> struct nvme_tcp_request async_req;
> u32 io_queues[HCTX_MAX_TYPES];
> +
> + struct net_device *ddp_netdev;
> + u32 ddp_threshold;
> +#ifdef CONFIG_ULP_DDP
> + struct ulp_ddp_limits ddp_limits;
> +#endif
> };
>
> static LIST_HEAD(nvme_tcp_ctrl_list);
> @@ -291,6 +324,166 @@ static inline size_t nvme_tcp_pdu_last_send(struct nvme_tcp_request *req,
> return nvme_tcp_pdu_data_left(req) <= len;
> }
>
> +#ifdef CONFIG_ULP_DDP
> +
> +static struct net_device *
> +nvme_tcp_get_ddp_netdev_with_limits(struct nvme_tcp_ctrl *ctrl)
> +{
> + struct net_device *netdev;
> + bool ok;
> +
> + if (!ddp_offload)
> + return NULL;
> +
> + /* netdev ref is put in nvme_tcp_stop_admin_queue() */
> + netdev = get_netdev_for_sock(ctrl->queues[0].sock->sk);
> + if (!netdev) {
> + dev_dbg(ctrl->ctrl.device, "netdev not found\n");
> + return NULL;
> + }
> +
> + ok = ulp_ddp_query_limits(netdev, &ctrl->ddp_limits,
> + ULP_DDP_NVME, ULP_DDP_CAP_NVME_TCP,
> + ctrl->ctrl.opts->tls);
> + if (!ok) {

please use a normal name (ret).

Plus, its strange that a query function receives a feature and returns
true/false based on this. The query should return the limits, and the
caller should look at the limits and see if it is appropriately
supported.

The rest looks fine I think.