From 0971374e2818eef6ebdbd7a37acf6ab7e98ac06c Mon Sep 17 00:00:00 2001 From: Trond Myklebust Date: Thu, 24 Jul 2014 23:59:31 -0400 Subject: [PATCH] SUNRPC: Reduce contention in svc_xprt_enqueue() Ensure that all calls to svc_xprt_enqueue() except svc_xprt_received() check the value of XPT_BUSY, before attempting to grab spinlocks etc. This is to avoid situations such as the following "perf" trace, which shows heavy contention on the pool spinlock: 54.15% nfsd [kernel.kallsyms] [k] _raw_spin_lock_bh | --- _raw_spin_lock_bh | |--71.43%-- svc_xprt_enqueue | | | |--50.31%-- svc_reserve | | | |--31.35%-- svc_xprt_received | | | |--18.34%-- svc_tcp_data_ready ... Signed-off-by: Trond Myklebust Signed-off-by: J. Bruce Fields --- net/sunrpc/svc_xprt.c | 25 +++++++++++++++++-------- 1 file changed, 17 insertions(+), 8 deletions(-) diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c index b4737fbdec13..9cfa391e2bd0 100644 --- a/net/sunrpc/svc_xprt.c +++ b/net/sunrpc/svc_xprt.c @@ -23,6 +23,7 @@ static int svc_deferred_recv(struct svc_rqst *rqstp); static struct cache_deferred_req *svc_defer(struct cache_req *req); static void svc_age_temp_xprts(unsigned long closure); static void svc_delete_xprt(struct svc_xprt *xprt); +static void svc_xprt_do_enqueue(struct svc_xprt *xprt); /* apparently the "standard" is that clients close * idle connections after 5 minutes, servers after @@ -222,11 +223,12 @@ static void svc_xprt_received(struct svc_xprt *xprt) if (!test_bit(XPT_BUSY, &xprt->xpt_flags)) return; /* As soon as we clear busy, the xprt could be closed and - * 'put', so we need a reference to call svc_xprt_enqueue with: + * 'put', so we need a reference to call svc_xprt_do_enqueue with: */ svc_xprt_get(xprt); + smp_mb__before_atomic(); clear_bit(XPT_BUSY, &xprt->xpt_flags); - svc_xprt_enqueue(xprt); + svc_xprt_do_enqueue(xprt); svc_xprt_put(xprt); } @@ -335,12 +337,7 @@ static bool svc_xprt_has_something_to_do(struct svc_xprt *xprt) return false; } -/* - * Queue up a transport with data pending. If there are idle nfsd - * processes, wake 'em up. - * - */ -void svc_xprt_enqueue(struct svc_xprt *xprt) +static void svc_xprt_do_enqueue(struct svc_xprt *xprt) { struct svc_pool *pool; struct svc_rqst *rqstp; @@ -398,6 +395,18 @@ void svc_xprt_enqueue(struct svc_xprt *xprt) out_unlock: spin_unlock_bh(&pool->sp_lock); } + +/* + * Queue up a transport with data pending. If there are idle nfsd + * processes, wake 'em up. + * + */ +void svc_xprt_enqueue(struct svc_xprt *xprt) +{ + if (test_bit(XPT_BUSY, &xprt->xpt_flags)) + return; + svc_xprt_do_enqueue(xprt); +} EXPORT_SYMBOL_GPL(svc_xprt_enqueue); /* -- 2.39.5