[PATCH net-next] netpoll: more efficient locking
From: Eric Dumazet <hidden>
Date: 2016-11-16 22:54:52
From: Eric Dumazet <edumazet@google.com>
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 <edumazet@google.com>
---
include/linux/netdevice.h | 1 -
include/linux/netpoll.h | 13 +++++++------
net/core/dev.c | 1 -
net/core/netpoll.c | 6 +++---
4 files changed, 10 insertions(+), 11 deletions(-)
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index bcddf951ccee..e84800edd249 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h@@ -316,7 +316,6 @@ struct napi_struct { unsigned int gro_count; int (*poll)(struct napi_struct *, int); #ifdef CONFIG_NETPOLL - spinlock_t poll_lock; int poll_owner; #endif struct net_device *dev;
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)
diff --git a/net/core/dev.c b/net/core/dev.c
index edba9efeb2e9..f71b34ab57a5 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c@@ -5143,7 +5143,6 @@ void netif_napi_add(struct net_device *dev, struct napi_struct *napi, list_add(&napi->dev_list, &dev->napi_list); napi->dev = dev; #ifdef CONFIG_NETPOLL - spin_lock_init(&napi->poll_lock); napi->poll_owner = -1; #endif set_bit(NAPI_STATE_SCHED, &napi->state);
diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index 53599bd0c82d..9424673009c1 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c@@ -171,12 +171,12 @@ static void poll_one_napi(struct napi_struct *napi) static void poll_napi(struct net_device *dev) { struct napi_struct *napi; + int cpu = smp_processor_id(); list_for_each_entry(napi, &dev->napi_list, dev_list) { - if (napi->poll_owner != smp_processor_id() && - spin_trylock(&napi->poll_lock)) { + if (cmpxchg(&napi->poll_owner, -1, cpu) == -1) { poll_one_napi(napi); - spin_unlock(&napi->poll_lock); + smp_store_release(&napi->poll_owner, -1); } } }