> On Feb 8, 2017, at 7:05 PM, Trond Myklebust <trondmy@xxxxxxxxxxxxxxx> wrote:
>
> On Wed, 2017-02-08 at 17:01 -0500, Chuck Lever wrote:
>> Allow RPC-over-RDMA to send NULL pings even when the transport has
>> hit its credit limit. One RPC-over-RDMA credit is reserved for
>> operations like keepalive.
>>
>> For transports that convey NFSv4, it seems like lease renewal would
>> also be a candidate for using a priority transport slot. I'd like to
>> see a mechanism better than RPCRDMA_PRIORITY that can ensure only
>> one priority operation is in use at a time.
>>
>> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
>> ---
>> include/linux/sunrpc/sched.h | 2 ++
>> net/sunrpc/xprt.c | 4 ++++
>> net/sunrpc/xprtrdma/transport.c | 3 ++-
>> net/sunrpc/xprtrdma/verbs.c | 13 ++++++++-----
>> 4 files changed, 16 insertions(+), 6 deletions(-)
>>
>> diff --git a/include/linux/sunrpc/sched.h
>> b/include/linux/sunrpc/sched.h
>> index 13822e6..fcea158 100644
>> --- a/include/linux/sunrpc/sched.h
>> +++ b/include/linux/sunrpc/sched.h
>> @@ -127,6 +127,7 @@ struct rpc_task_setup {
>> #define RPC_TASK_TIMEOUT 0x1000 /* fail with
>> ETIMEDOUT on timeout */
>> #define RPC_TASK_NOCONNECT 0x2000 /* return
>> ENOTCONN if not connected */
>> #define RPC_TASK_NO_RETRANS_TIMEOUT 0x4000 /*
>> wait forever for a reply */
>> +#define RPC_TASK_NO_CONG 0x8000 /* skip
>> congestion control */
>>
>> #define RPC_TASK_SOFTPING (RPC_TASK_SOFT | RPC_TASK_SOFTCONN)
>>
>> @@ -137,6 +138,7 @@ struct rpc_task_setup {
>> #define RPC_IS_SOFT(t) ((t)->tk_flags &
>> (RPC_TASK_SOFT|RPC_TASK_TIMEOUT))
>> #define RPC_IS_SOFTCONN(t) ((t)->tk_flags &
>> RPC_TASK_SOFTCONN)
>> #define RPC_WAS_SENT(t) ((t)->tk_flags &
>> RPC_TASK_SENT)
>> +#define RPC_SKIP_CONG(t) ((t)->tk_flags & RPC_TASK_NO_CONG)
>>
>> #define RPC_TASK_RUNNING 0
>> #define RPC_TASK_QUEUED 1
>> diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
>> index b530a28..a477ee6 100644
>> --- a/net/sunrpc/xprt.c
>> +++ b/net/sunrpc/xprt.c
>> @@ -392,6 +392,10 @@ static inline void xprt_release_write(struct
>> rpc_xprt *xprt, struct rpc_task *ta
>> {
>> struct rpc_rqst *req = task->tk_rqstp;
>>
>> + if (RPC_SKIP_CONG(task)) {
>> + req->rq_cong = 0;
>> + return 1;
>> + }
>
> Why not just have the RDMA layer call xprt_reserve_xprt() (and
> xprt_release_xprt()) if this flag is set? It seems to me that you will
> need some kind of extra congestion control in the RDMA layer anyway
> since you only have one reserved credit for these privileged tasks (or
> did I miss where that is being gated?).
Thanks for the review.
See RPCRDMA_IA_RSVD_CREDIT in 11/12. It's a hack I'm not
terribly happy with.
So, I think you are suggesting replacing xprtrdma's
->reserve_xprt with something like:
int xprt_rdma_reserve_xprt(xprt, task)
{
if (RPC_SKIP_CONG(task))
return xprt_reserve_xprt(xprt, task);
return xprt_reserve_xprt_cong(xprt, task);
}
and likewise for ->release_xprt ?
What I'd really like to do is have the RPC layer
prevent more than one RPC at a time from using the
extra credit, and somehow ensure that those RPCs
are going to be short-lived (SOFT | SOFTCONN,
maybe).
>> if (req->rq_cong)
>> return 1;
>> dprintk("RPC: %5u xprt_cwnd_limited cong = %lu cwnd =
>> %lu\n",
>> diff --git a/net/sunrpc/xprtrdma/transport.c
>> b/net/sunrpc/xprtrdma/transport.c
>> index 3a5a805..073fecd 100644
>> --- a/net/sunrpc/xprtrdma/transport.c
>> +++ b/net/sunrpc/xprtrdma/transport.c
>> @@ -546,7 +546,8 @@ static void rpcrdma_keepalive_release(void
>> *calldata)
>>
>> data = xprt_get(xprt);
>> null_task = rpc_call_null_helper(task->tk_client, xprt,
>> NULL,
>> - RPC_TASK_SOFTPING |
>> RPC_TASK_ASYNC,
>> + RPC_TASK_SOFTPING |
>> RPC_TASK_ASYNC |
>> + RPC_TASK_NO_CONG,
>> &rpcrdma_keepalive_call_ops
>> , data);
>> if (!IS_ERR(null_task))
>> rpc_put_task(null_task);
>> diff --git a/net/sunrpc/xprtrdma/verbs.c
>> b/net/sunrpc/xprtrdma/verbs.c
>> index 81cd31a..d9b5fa7 100644
>> --- a/net/sunrpc/xprtrdma/verbs.c
>> +++ b/net/sunrpc/xprtrdma/verbs.c
>> @@ -136,19 +136,20 @@
>> 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;
>> + __be32 *p = rep->rr_rdmabuf->rg_base;
>> u32 credits;
>>
>> if (rep->rr_len < RPCRDMA_HDRLEN_ERR)
>> return;
>>
>> - credits = be32_to_cpu(rmsgp->rm_credit);
>> + credits = be32_to_cpup(p + 2);
>> + if (credits > buffer->rb_max_requests)
>> + credits = buffer->rb_max_requests;
>> + /* Reserve one credit for keepalive ping */
>> + credits--;
>> 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);
>> }
>>
>> @@ -915,6 +916,8 @@ struct rpcrdma_rep *
>> struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
>> int i, rc;
>>
>> + if (r_xprt->rx_data.max_requests < 2)
>> + return -EINVAL;
>> buf->rb_max_requests = r_xprt->rx_data.max_requests;
>> buf->rb_bc_srv_max_requests = 0;
>> atomic_set(&buf->rb_credits, 1);
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-nfs"
>> in
>> the body of a message to majordomo@xxxxxxxxxxxxxxx
>> More majordomo info at http://vger.kernel.org/majordomo-info.html
>>
> --
>
>
>
>
>
>
> Trond Myklebust
> Principal System Architect
> 4300 El Camino Real | Suite 100
> Los Altos, CA 94022
> W: 650-422-3800
> C: 801-921-4583
> www.primarydata.com
--
Chuck Lever
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