Re: [PATCH 3/7] SUNRPC: Clean up call_transmit_status()

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On Oct 7, 2009, at 6:22 PM, Trond Myklebust wrote:
On Wed, 2009-10-07 at 18:02 -0400, Chuck Lever wrote:
Clean up: re-arrange the cases in call_transmit_status() to make the
code easier to read.

Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
---

net/sunrpc/clnt.c |   24 ++++++++++++------------
1 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index 57f39b7..c26669c 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -1175,25 +1175,21 @@ call_transmit(struct rpc_task *task)

/*
 * 5a.	Handle cleanup after a transmission
+ *	If we've been waiting on the socket's write_space()
+ *	callback, or if the server is temporarily unreachable,
+ *	continue holding the transport lock.
 */
static void
call_transmit_status(struct rpc_task *task)
{
+	dprint_status(task);
+
	task->tk_action = call_status;
+
	switch (task->tk_status) {
-	case -EAGAIN:
-		break;
-	default:
-		xprt_end_transmit(task);
-		rpc_task_force_reencode(task);
+	case -EAGAIN:			/* no write space */
		break;
-		/*
-		 * Special cases: if we've been waiting on the
-		 * socket's write_space() callback, or if the
-		 * socket just returned a connection error,
-		 * then hold onto the transport lock.
-		 */
-	case -ECONNREFUSED:
+	case -ECONNREFUSED:		/* connection problems */
	case -ECONNRESET:
	case -ENOTCONN:
	case -EHOSTDOWN:
@@ -1206,6 +1202,10 @@ call_transmit_status(struct rpc_task *task)
			break;
		}
		rpc_task_force_reencode(task);
+		break;
+	default:			/* success, or some other error */
+		xprt_end_transmit(task);
+		rpc_task_force_reencode(task);
	}
}

This puts the most common case (success) at the very end of the switch
statement. Most compilers will generate the most efficient code when it
is at the very beginning...

I dropped this one, since it's not that important.

But I wouldn't expect the compiler could optimize the default: case the way you described. No matter what order you write these in, the code has to check each of the other cases first before deciding to execute the default: arm. If it's that important, maybe we should add a "case 0:" arm?


Trond


--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com



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