Hey Chuck,
On 01/07/2015 06:12 PM, Chuck Lever wrote:
> Reduce work in the receive CQ handler, which is run at hardware
> interrupt level, by moving the RPC/RDMA credit update logic to the
> RPC reply handler.
>
> This has some additional benefits: More header sanity checking is
> done before trusting the incoming credit value, and the receive CQ
> handler no longer touches the RPC/RDMA header. Finally, no longer
> any need to update and read rb_credits atomically, so the rb_credits
> field can be removed.
>
> This further extends work begun by commit e7ce710a8802 ("xprtrdma:
> Avoid deadlock when credit window is reset").
>
> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> ---
> net/sunrpc/xprtrdma/rpc_rdma.c | 10 ++++++++--
> net/sunrpc/xprtrdma/verbs.c | 15 ++-------------
> net/sunrpc/xprtrdma/xprt_rdma.h | 1 -
> 3 files changed, 10 insertions(+), 16 deletions(-)
>
> diff --git a/net/sunrpc/xprtrdma/rpc_rdma.c b/net/sunrpc/xprtrdma/rpc_rdma.c
> index dcf5ebc..d731010 100644
> --- a/net/sunrpc/xprtrdma/rpc_rdma.c
> +++ b/net/sunrpc/xprtrdma/rpc_rdma.c
> @@ -736,7 +736,7 @@ rpcrdma_reply_handler(struct rpcrdma_rep *rep)
> struct rpc_xprt *xprt = rep->rr_xprt;
> struct rpcrdma_xprt *r_xprt = rpcx_to_rdmax(xprt);
> __be32 *iptr;
> - int rdmalen, status;
> + int credits, rdmalen, status;
> unsigned long cwnd;
>
> /* Check status. If bad, signal disconnect and return rep to pool */
> @@ -871,8 +871,14 @@ badheader:
> break;
> }
>
> + credits = be32_to_cpu(headerp->rm_credit);
> + if (credits == 0)
> + credits = 1; /* don't deadlock */
> + else if (credits > r_xprt->rx_buf.rb_max_requests)
> + credits = r_xprt->rx_buf.rb_max_requests;
Can rb_max_requests ever drop to 0?
Anna
> +
> cwnd = xprt->cwnd;
> - xprt->cwnd = atomic_read(&r_xprt->rx_buf.rb_credits) << RPC_CWNDSHIFT;
> + xprt->cwnd = credits << RPC_CWNDSHIFT;
> if (xprt->cwnd > cwnd)
> xprt_release_rqst_cong(rqst->rq_task);
>
> diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
> index 1000f63..71a071a 100644
> --- a/net/sunrpc/xprtrdma/verbs.c
> +++ b/net/sunrpc/xprtrdma/verbs.c
> @@ -49,6 +49,7 @@
>
> #include <linux/interrupt.h>
> #include <linux/slab.h>
> +#include <linux/prefetch.h>
> #include <asm/bitops.h>
>
> #include "xprt_rdma.h"
> @@ -298,17 +299,7 @@ rpcrdma_recvcq_process_wc(struct ib_wc *wc, struct list_head *sched_list)
> rep->rr_len = wc->byte_len;
> ib_dma_sync_single_for_cpu(rdmab_to_ia(rep->rr_buffer)->ri_id->device,
> rep->rr_iov.addr, rep->rr_len, DMA_FROM_DEVICE);
> -
> - if (rep->rr_len >= 16) {
> - struct rpcrdma_msg *p = (struct rpcrdma_msg *)rep->rr_base;
> - unsigned int credits = ntohl(p->rm_credit);
> -
> - if (credits == 0)
> - credits = 1; /* don't deadlock */
> - else if (credits > rep->rr_buffer->rb_max_requests)
> - credits = rep->rr_buffer->rb_max_requests;
> - atomic_set(&rep->rr_buffer->rb_credits, credits);
> - }
> + prefetch(rep->rr_base);
>
> out_schedule:
> list_add_tail(&rep->rr_list, sched_list);
> @@ -480,7 +471,6 @@ rpcrdma_conn_upcall(struct rdma_cm_id *id, struct rdma_cm_event *event)
> case RDMA_CM_EVENT_DEVICE_REMOVAL:
> connstate = -ENODEV;
> connected:
> - atomic_set(&rpcx_to_rdmax(ep->rep_xprt)->rx_buf.rb_credits, 1);
> dprintk("RPC: %s: %sconnected\n",
> __func__, connstate > 0 ? "" : "dis");
> ep->rep_connected = connstate;
> @@ -1186,7 +1176,6 @@ rpcrdma_buffer_create(struct rpcrdma_buffer *buf, struct rpcrdma_ep *ep,
>
> buf->rb_max_requests = cdata->max_requests;
> spin_lock_init(&buf->rb_lock);
> - atomic_set(&buf->rb_credits, 1);
>
> /* Need to allocate:
> * 1. arrays for send and recv pointers
> diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h
> index 532d586..3fcc92b 100644
> --- a/net/sunrpc/xprtrdma/xprt_rdma.h
> +++ b/net/sunrpc/xprtrdma/xprt_rdma.h
> @@ -248,7 +248,6 @@ struct rpcrdma_req {
> */
> struct rpcrdma_buffer {
> spinlock_t rb_lock; /* protects indexes */
> - atomic_t rb_credits; /* most recent server credits */
> int rb_max_requests;/* client max requests */
> struct list_head rb_mws; /* optional memory windows/fmrs/frmrs */
> struct list_head rb_all;
>
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