From 61a5ff15ebdab87887861a6b128b108404e4706d Mon Sep 17 00:00:00 2001 From: Amos Kong Date: Thu, 9 Jun 2011 00:27:10 -0700 Subject: [PATCH] tun: do not put self in waitq if doing a nonblock read Perf shows a relatively high rate (about 8%) race in spin_lock_irqsave() when doing netperf between external host and guest. It's mainly becuase the lock contention between the tun_do_read() and tun_xmit_skb(), so this patch do not put self into waitqueue to reduce this kind of race. After this patch, it drops to 4%. Signed-off-by: Jason Wang Signed-off-by: Amos Kong Signed-off-by: David S. Miller --- drivers/net/tun.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/net/tun.c b/drivers/net/tun.c index 2829badbae38..ef68e13c042d 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -817,7 +817,8 @@ static ssize_t tun_do_read(struct tun_struct *tun, tun_debug(KERN_INFO, tun, "tun_chr_read\n"); - add_wait_queue(&tun->wq.wait, &wait); + if (unlikely(!noblock)) + add_wait_queue(&tun->wq.wait, &wait); while (len) { current->state = TASK_INTERRUPTIBLE; @@ -848,7 +849,8 @@ static ssize_t tun_do_read(struct tun_struct *tun, } current->state = TASK_RUNNING; - remove_wait_queue(&tun->wq.wait, &wait); + if (unlikely(!noblock)) + remove_wait_queue(&tun->wq.wait, &wait); return ret; }