SUNRPC: Add trace event that reports reply page vector alignment

We don't want READ payloads that are partially in the head iovec and
in the page buffer because this requires pull-up, which can be
expensive.

The NFS/RPC client tries hard to predict the size of the head iovec
so that the incoming READ data payload lands only in the page
vector, but it doesn't always get it right. To help diagnose such
problems, add a trace point in the logic that decodes READ-like
operations that reports whether pull-up is being done.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

1 files changed, 59 insertions, 0 deletions

diff --git a/include/trace/events/sunrpc.h b/include/trace/events/sunrpc.h
index fbc41b8142d3..627650800676 100644
--- a/include/trace/events/sunrpc.h
+++ b/include/trace/events/sunrpc.h
@@ -321,6 +321,65 @@ TRACE_EVENT(rpc_xdr_overflow,
 	)
 );
 
+TRACE_EVENT(rpc_xdr_alignment,
+	TP_PROTO(
+		const struct xdr_stream *xdr,
+		size_t offset,
+		unsigned int copied
+	),
+
+	TP_ARGS(xdr, offset, copied),
+
+	TP_STRUCT__entry(
+		__field(unsigned int, task_id)
+		__field(unsigned int, client_id)
+		__field(int, version)
+		__field(size_t, offset)
+		__field(unsigned int, copied)
+		__field(const void *, head_base)
+		__field(size_t, head_len)
+		__field(const void *, tail_base)
+		__field(size_t, tail_len)
+		__field(unsigned int, page_len)
+		__field(unsigned int, len)
+		__string(progname,
+			 xdr->rqst->rq_task->tk_client->cl_program->name)
+		__string(procedure,
+			 xdr->rqst->rq_task->tk_msg.rpc_proc->p_name)
+	),
+
+	TP_fast_assign(
+		const struct rpc_task *task = xdr->rqst->rq_task;
+
+		__entry->task_id = task->tk_pid;
+		__entry->client_id = task->tk_client->cl_clid;
+		__assign_str(progname,
+			     task->tk_client->cl_program->name)
+		__entry->version = task->tk_client->cl_vers;
+		__assign_str(procedure, task->tk_msg.rpc_proc->p_name)
+
+		__entry->offset = offset;
+		__entry->copied = copied;
+		__entry->head_base = xdr->buf->head[0].iov_base,
+		__entry->head_len = xdr->buf->head[0].iov_len,
+		__entry->page_len = xdr->buf->page_len,
+		__entry->tail_base = xdr->buf->tail[0].iov_base,
+		__entry->tail_len = xdr->buf->tail[0].iov_len,
+		__entry->len = xdr->buf->len;
+	),
+
+	TP_printk(
+		"task:%u@%u %sv%d %s offset=%zu copied=%u xdr=[%p,%zu]/%u/[%p,%zu]/%u\n",
+		__entry->task_id, __entry->client_id,
+		__get_str(progname), __entry->version, __get_str(procedure),
+		__entry->offset, __entry->copied,
+		__entry->head_base, __entry->head_len,
+		__entry->page_len,
+		__entry->tail_base, __entry->tail_len,
+		__entry->len
+	)
+);
+
 /*
  * First define the enums in the below macros to be exported to userspace
  * via TRACE_DEFINE_ENUM().