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netpoll: more efficient locking

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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: 217f697436 ("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>
This commit is contained in:
Eric Dumazet
2016-11-16 14:54:50 -08:00
committed by David S. Miller
parent 1629dd4f76
commit 89c4b442b7
4 changed files with 10 additions and 11 deletions
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6
net/core/netpoll.c
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@@ -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);
}
}
}