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| author | Chuck Lever <chuck.lever@oracle.com> | 2026-03-24 09:04:49 -0400 |
|---|---|---|
| committer | Chuck Lever <chuck.lever@oracle.com> | 2026-05-28 11:31:26 -0400 |
| commit | c9f3f22ab7a9549dfa76f173f3c75b684e103a08 (patch) | |
| tree | 17e4af3296323b1c826f9cc9445dca9d2316d9b8 /net | |
| parent | 491efd53855b3d92f46b8e9ac5df66a93f59447e (diff) | |
| download | linux-next-history-c9f3f22ab7a9549dfa76f173f3c75b684e103a08.tar.gz | |
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>
Diffstat (limited to 'net')
| -rw-r--r-- | net/sunrpc/svc_xprt.c | 13 |
1 files changed, 10 insertions, 3 deletions
diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c index 377f5d7490aa4..63d1002e63e74 100644 --- a/net/sunrpc/svc_xprt.c +++ b/net/sunrpc/svc_xprt.c @@ -440,16 +440,23 @@ static bool svc_xprt_reserve_slot(struct svc_rqst *rqstp, struct svc_xprt *xprt) /* * After a caller releases write-space or a request slot, * re-enqueue the transport only when there is pending - * work that a thread could act on. The smp_mb() pairs + * work that a thread could act on. The smp_mb() pairs * with the smp_rmb() in svc_xprt_ready() and orders the * preceding counter update before the flags read so a * concurrent set_bit(XPT_DATA) is visible here. + * + * When the transport is BUSY, the thread holding it will + * call svc_xprt_received() upon completion, which checks + * for pending work and re-enqueues as needed. */ static void svc_xprt_resource_released(struct svc_xprt *xprt) { + unsigned long xpt_flags; + smp_mb(); - if (READ_ONCE(xprt->xpt_flags) & - (BIT(XPT_DATA) | BIT(XPT_DEFERRED))) + xpt_flags = READ_ONCE(xprt->xpt_flags); + if (xpt_flags & (BIT(XPT_DATA) | BIT(XPT_DEFERRED)) && + !(xpt_flags & BIT(XPT_BUSY))) svc_xprt_enqueue(xprt); } |