From 206a134b4d8abf57cd34dffacf993869355b9aac Mon Sep 17 00:00:00 2001 From: Chuck Lever Date: Thu, 3 Dec 2009 15:58:56 -0500 Subject: SUNRPC: Check explicitly for tk_status == 0 in call_transmit_status() The success case, where task->tk_status == 0, is by far the most frequent case in call_transmit_status(). The default: arm of the switch statement in call_transmit_status() handles the 0 case. default: was moved close to the top of the switch statement in call_transmit_status() under the theory that the compiler places object code for the earliest arms of a switch statement first, making the CPU do less work. The default: arm of a switch statement, however, is executed only after all the other cases have been checked. Even if the compiler rearranges the object code, the default: arm is the "last resort", meaning all of the other cases have been explicitly exhausted. That makes the current arrangement about as inefficient as it gets for the common case. To fix this, add an explicit check for zero before the switch statement. That forces the compiler to do the zero check first, no matter what optimizations it might try to do to the switch statement. Signed-off-by: Chuck Lever Signed-off-by: Trond Myklebust --- net/sunrpc/clnt.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c index 38829e20500b..7bcd931e06ee 100644 --- a/net/sunrpc/clnt.c +++ b/net/sunrpc/clnt.c @@ -1180,10 +1180,22 @@ static void call_transmit_status(struct rpc_task *task) { task->tk_action = call_status; + + /* + * Common case: success. Force the compiler to put this + * test first. + */ + if (task->tk_status == 0) { + xprt_end_transmit(task); + rpc_task_force_reencode(task); + return; + } + switch (task->tk_status) { case -EAGAIN: break; default: + dprint_status(task); xprt_end_transmit(task); /* * Special cases: if we've been waiting on the -- cgit v1.2.3