> On Feb 15, 2016, at 9:29 AM, Devesh Sharma <devesh.sharma@xxxxxxxxxxxx> wrote:
>
> On Sat, Feb 13, 2016 at 2:36 AM, Chuck Lever <chuck.lever@xxxxxxxxxx> wrote:
>> Commit fe97b47cd623 ("xprtrdma: Use workqueue to process RPC/RDMA
>> replies") replaced the reply tasklet with a workqueue that allows
>> RPC replies to be processed in parallel. Thus the credit values in
>> RPC-over-RDMA replies can applied in a different order than in
>> which the server sent them.
>>
>> To fix this, revert commit eba8ff660b2d ("xprtrdma: Move credit
>> update to RPC reply handler"). Done by hand to accommodate code
>> changes that have occurred since then.
>>
>> Fixes: fe97b47cd623 ("xprtrdma: Use workqueue to process . . .")
>> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
>> ---
>> net/sunrpc/xprtrdma/rpc_rdma.c | 9 +--------
>> net/sunrpc/xprtrdma/verbs.c | 27 ++++++++++++++++++++++++++-
>> net/sunrpc/xprtrdma/xprt_rdma.h | 1 +
>> 3 files changed, 28 insertions(+), 9 deletions(-)
>>
>> diff --git a/net/sunrpc/xprtrdma/rpc_rdma.c b/net/sunrpc/xprtrdma/rpc_rdma.c
>> index c341225..0c45288 100644
>> --- a/net/sunrpc/xprtrdma/rpc_rdma.c
>> +++ b/net/sunrpc/xprtrdma/rpc_rdma.c
>> @@ -797,7 +797,6 @@ rpcrdma_reply_handler(struct rpcrdma_rep *rep)
>> __be32 *iptr;
>> int rdmalen, status, rmerr;
>> unsigned long cwnd;
>> - u32 credits;
>>
>> dprintk("RPC: %s: incoming rep %p\n", __func__, rep);
>
> You may also want to remove the extra header len checks from here.
> Header len validity is already checked
> in rpcrdma_update_granted_credits() function call before scheduling wq.
Actually we need to repost a receive buffer for these
error cases, and it doesn't look like this is done
consistently in the current logic.
>> @@ -930,15 +929,9 @@ out:
>> if (req->rl_nchunks)
>> r_xprt->rx_ia.ri_ops->ro_unmap_sync(r_xprt, req);
>>
>> - 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;
>> -
>> spin_lock_bh(&xprt->transport_lock);
>> cwnd = xprt->cwnd;
>> - xprt->cwnd = credits << RPC_CWNDSHIFT;
>> + xprt->cwnd = atomic_read(&r_xprt->rx_buf.rb_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 878f1bf..fc1ef5f 100644
>> --- a/net/sunrpc/xprtrdma/verbs.c
>> +++ b/net/sunrpc/xprtrdma/verbs.c
>> @@ -190,6 +190,28 @@ rpcrdma_receive_worker(struct work_struct *work)
>> rpcrdma_reply_handler(rep);
>> }
>>
>> +/* Perform basic sanity checking to avoid using garbage
>> + * to update the credit grant value.
>> + */
>> +static void
>> +rpcrdma_update_granted_credits(struct rpcrdma_rep *rep)
>> +{
>> + struct rpcrdma_msg *rmsgp = rdmab_to_msg(rep->rr_rdmabuf);
>> + struct rpcrdma_buffer *buffer = &rep->rr_rxprt->rx_buf;
>> + u32 credits;
>> +
>> + if (rep->rr_len < RPCRDMA_HDRLEN_ERR)
>> + return;
>> +
>> + credits = be32_to_cpu(rmsgp->rm_credit);
>> + if (credits == 0)
>> + credits = 1; /* don't deadlock */
>> + else if (credits > buffer->rb_max_requests)
>> + credits = buffer->rb_max_requests;
>> +
>> + atomic_set(&buffer->rb_credits, credits);
>> +}
>> +
>> static void
>> rpcrdma_recvcq_process_wc(struct ib_wc *wc)
>> {
>> @@ -211,7 +233,8 @@ rpcrdma_recvcq_process_wc(struct ib_wc *wc)
>> ib_dma_sync_single_for_cpu(rep->rr_device,
>> rdmab_addr(rep->rr_rdmabuf),
>> rep->rr_len, DMA_FROM_DEVICE);
>> - prefetch(rdmab_to_msg(rep->rr_rdmabuf));
>
> do you really want to remove prefetch()?
Yes. Parsing the credits field in the header amounts to
the same thing, the header content is pulled into the
CPU cache.
>> +
>> + rpcrdma_update_granted_credits(rep);
>>
>> out_schedule:
>> queue_work(rpcrdma_receive_wq, &rep->rr_work);
>> @@ -330,6 +353,7 @@ rpcrdma_conn_upcall(struct rdma_cm_id *id, struct rdma_cm_event *event)
>> connected:
>> dprintk("RPC: %s: %sconnected\n",
>> __func__, connstate > 0 ? "" : "dis");
>> + atomic_set(&xprt->rx_buf.rb_credits, 1);
>> ep->rep_connected = connstate;
>> rpcrdma_conn_func(ep);
>> wake_up_all(&ep->rep_connect_wait);
>> @@ -943,6 +967,7 @@ rpcrdma_buffer_create(struct rpcrdma_xprt *r_xprt)
>> buf->rb_max_requests = r_xprt->rx_data.max_requests;
>> buf->rb_bc_srv_max_requests = 0;
>> spin_lock_init(&buf->rb_lock);
>> + atomic_set(&buf->rb_credits, 1);
>
> Will this give a slow start to server initially? should it be rb_max_requests?
> I am not sure, just raising a flag to bring your notice.
Starting at 1 is required by RFC 5666.
It's not slow start. The first server reply should contain
a large credit value, which takes effect as soon as the
receive WC is processed.
>> rc = ia->ri_ops->ro_init(r_xprt);
>> if (rc)
>> diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h
>> index bf98c67..efd6fa7 100644
>> --- a/net/sunrpc/xprtrdma/xprt_rdma.h
>> +++ b/net/sunrpc/xprtrdma/xprt_rdma.h
>> @@ -312,6 +312,7 @@ struct rpcrdma_buffer {
>> struct list_head rb_send_bufs;
>> struct list_head rb_recv_bufs;
>> u32 rb_max_requests;
>> + atomic_t rb_credits; /* most recent credit grant */
>>
>> u32 rb_bc_srv_max_requests;
>> spinlock_t rb_reqslock; /* protect rb_allreqs */
>>
>> --
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--
Chuck Lever
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