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svcrdma: Don't account for Receive queue "starvation"

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>From what I can tell, calling ->recvfrom when there is no work to do
is a normal part of operation. This is the only way svc_recv can
tell when there is no more data ready to receive on the transport.

Neither the TCP nor the UDP transport implementations have a
"starve" metric.

The cost of receive starvation accounting is bumping an atomic, which
results in extra (IMO unnecessary) bus traffic between CPU sockets,
while holding a spin lock.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
This commit is contained in:
Chuck Lever
2017-06-23 17:18:08 -04:00
committed by J. Bruce Fields
parent ca5c76aba7
commit 2d6491a56c
1 changed files with 6 additions and 15 deletions
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21
net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
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@@ -844,9 +844,9 @@ int svc_rdma_recvfrom(struct svc_rqst *rqstp)
struct svc_xprt *xprt = rqstp->rq_xprt; struct svc_xprt *xprt = rqstp->rq_xprt;
struct svcxprt_rdma *rdma_xprt = struct svcxprt_rdma *rdma_xprt =
container_of(xprt, struct svcxprt_rdma, sc_xprt); container_of(xprt, struct svcxprt_rdma, sc_xprt);
struct svc_rdma_op_ctxt *ctxt = NULL; struct svc_rdma_op_ctxt *ctxt;
struct rpcrdma_msg *rmsgp; struct rpcrdma_msg *rmsgp;
int ret = 0; int ret;
dprintk("svcrdma: rqstp=%p\n", rqstp); dprintk("svcrdma: rqstp=%p\n", rqstp);
@@ -863,21 +863,13 @@ int svc_rdma_recvfrom(struct svc_rqst *rqstp)
struct svc_rdma_op_ctxt, list); struct svc_rdma_op_ctxt, list);
list_del(&ctxt->list); list_del(&ctxt->list);
} else { } else {
atomic_inc(&rdma_stat_rq_starve); /* No new incoming requests, terminate the loop */
clear_bit(XPT_DATA, &xprt->xpt_flags); clear_bit(XPT_DATA, &xprt->xpt_flags);
ctxt = NULL; spin_unlock(&rdma_xprt->sc_rq_dto_lock);
return 0;
} }
spin_unlock(&rdma_xprt->sc_rq_dto_lock); spin_unlock(&rdma_xprt->sc_rq_dto_lock);
if (!ctxt) {
/* This is the EAGAIN path. The svc_recv routine will
* return -EAGAIN, the nfsd thread will go to call into
* svc_recv again and we shouldn't be on the active
* transport list
*/
if (test_bit(XPT_CLOSE, &xprt->xpt_flags))
goto defer;
goto out;
}
dprintk("svcrdma: processing ctxt=%p on xprt=%p, rqstp=%p\n", dprintk("svcrdma: processing ctxt=%p on xprt=%p, rqstp=%p\n",
ctxt, rdma_xprt, rqstp); ctxt, rdma_xprt, rqstp);
atomic_inc(&rdma_stat_recv); atomic_inc(&rdma_stat_recv);
@@ -920,7 +912,6 @@ complete:
+ rqstp->rq_arg.page_len + rqstp->rq_arg.page_len
+ rqstp->rq_arg.tail[0].iov_len; + rqstp->rq_arg.tail[0].iov_len;
svc_rdma_put_context(ctxt, 0); svc_rdma_put_context(ctxt, 0);
out:
dprintk("svcrdma: ret=%d, rq_arg.len=%u, " dprintk("svcrdma: ret=%d, rq_arg.len=%u, "
"rq_arg.head[0].iov_base=%p, rq_arg.head[0].iov_len=%zd\n", "rq_arg.head[0].iov_base=%p, rq_arg.head[0].iov_len=%zd\n",
ret, rqstp->rq_arg.len, ret, rqstp->rq_arg.len,