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| author | Eric Dumazet <edumazet@google.com> | 2016-11-16 14:54:50 -0800 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2016-11-16 18:32:02 -0500 |
| commit | 89c4b442b78bdba388337cc746fe63caba85f46c (patch) | |
| tree | 825a8d6e04cdc937950e9d8a79b52eeb249236c3 | |
| parent | 1629dd4f763cc15ac3b2711ac65dab153b738c6d (diff) | |
| download | linux-89c4b442b78bdba388337cc746fe63caba85f46c.tar.gz linux-89c4b442b78bdba388337cc746fe63caba85f46c.tar.bz2 linux-89c4b442b78bdba388337cc746fe63caba85f46c.zip | |
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 <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
| -rw-r--r-- | include/linux/netdevice.h | 1 | ||||
| -rw-r--r-- | include/linux/netpoll.h | 13 | ||||
| -rw-r--r-- | net/core/dev.c | 1 | ||||
| -rw-r--r-- | 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); } } } |