sunrpc: skip svc_xprt_enqueue when transport is busy

svc_xprt_resource_released() calls svc_xprt_enqueue()
whenever XPT_DATA or XPT_DEFERRED is set. During RPC
processing, svc_reserve_auth() reduces the reservation
counter and triggers this path while the current thread
still holds XPT_BUSY. The enqueue enters svc_xprt_ready(),
executes an smp_rmb(), READ_ONCE(), and tracepoint, then
returns false on seeing XPT_BUSY.

Trace data from a 256KB NFSv3 WRITE workload over TCP
shows this pattern generates roughly 195,000 wasted
enqueue calls -- approximately one per RPC -- each
paying the full svc_xprt_ready() cost for no benefit.

Add a BUSY check alongside the existing DATA|DEFERRED
check in svc_xprt_resource_released(). When the
transport is BUSY, the holder will call
svc_xprt_received() upon completion, which already
checks for pending work flags and re-enqueues.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

0 files changed, 0 insertions, 0 deletions