From cf1a1e07fc8bb29947ad3c9568d73aee3f851431 Mon Sep 17 00:00:00 2001 From: Paolo Abeni Date: Fri, 20 Apr 2018 13:18:16 +0200 Subject: [PATCH] tun: do not compute the rxhash, if not needed Currently, the tun driver, in absence of an eBPF steering program, always compute the rxhash in its rx path, even when such value is later unused due to additional checks ( This changeset moves the all the related checks just before the __skb_get_hash_symmetric(), so that the latter is no more computed when unneeded. Also replace an unneeded RCU section with rcu_access_pointer(). Signed-off-by: Paolo Abeni Acked-by: Jason Wang Signed-off-by: David S. Miller --- drivers/net/tun.c | 15 ++++++--------- 1 file changed, 6 insertions(+), 9 deletions(-) diff --git a/drivers/net/tun.c b/drivers/net/tun.c index 1e58be152d5c..091ace726763 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -525,11 +525,6 @@ static void tun_flow_update(struct tun_struct *tun, u32 rxhash, rcu_read_lock(); - /* We may get a very small possibility of OOO during switching, not - * worth to optimize.*/ - if (tun->numqueues == 1 || tfile->detached) - goto unlock; - e = tun_flow_find(head, rxhash); if (likely(e)) { /* TODO: keep queueing to old queue until it's empty? */ @@ -548,7 +543,6 @@ static void tun_flow_update(struct tun_struct *tun, u32 rxhash, spin_unlock_bh(&tun->lock); } -unlock: rcu_read_unlock(); } @@ -1937,10 +1931,13 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile, rcu_read_unlock(); } - rcu_read_lock(); - if (!rcu_dereference(tun->steering_prog)) + /* Compute the costly rx hash only if needed for flow updates. + * We may get a very small possibility of OOO during switching, not + * worth to optimize. + */ + if (!rcu_access_pointer(tun->steering_prog) && tun->numqueues > 1 && + !tfile->detached) rxhash = __skb_get_hash_symmetric(skb); - rcu_read_unlock(); if (frags) { /* Exercise flow dissector code path. */ -- 2.30.2