From 89c4b442b78bdba388337cc746fe63caba85f46c Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 16 Nov 2016 14:54:50 -0800 Subject: netpoll: more efficient locking Callers of netpoll_poll_lock() own NAPI_STATE_SCHED Callers of netpoll_poll_unlock() have BH blocked between the NAPI_STATE_SCHED being cleared and poll_lock is released. We can avoid the spinlock which has no contention, and use cmpxchg() on poll_owner which we need to set anyway. This removes a possible lockdep violation after the cited commit, since sk_busy_loop() re-enables BH before calling busy_poll_stop() Fixes: 217f69743681 ("net: busy-poll: allow preemption in sk_busy_loop()") Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- include/linux/netpoll.h | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) (limited to 'include/linux/netpoll.h') diff --git a/include/linux/netpoll.h b/include/linux/netpoll.h index b25ee9ffdbe6..1828900c9411 100644 --- a/include/linux/netpoll.h +++ b/include/linux/netpoll.h @@ -78,8 +78,11 @@ static inline void *netpoll_poll_lock(struct napi_struct *napi) struct net_device *dev = napi->dev; if (dev && dev->npinfo) { - spin_lock(&napi->poll_lock); - napi->poll_owner = smp_processor_id(); + int owner = smp_processor_id(); + + while (cmpxchg(&napi->poll_owner, -1, owner) != -1) + cpu_relax(); + return napi; } return NULL; @@ -89,10 +92,8 @@ static inline void netpoll_poll_unlock(void *have) { struct napi_struct *napi = have; - if (napi) { - napi->poll_owner = -1; - spin_unlock(&napi->poll_lock); - } + if (napi) + smp_store_release(&napi->poll_owner, -1); } static inline bool netpoll_tx_running(struct net_device *dev) -- cgit v1.2.3