diff options
| author | Amos Kong <akong@redhat.com> | 2011-06-09 00:27:10 -0700 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2011-06-09 00:27:10 -0700 |
| commit | 61a5ff15ebdab87887861a6b128b108404e4706d (patch) | |
| tree | e439d62aa7299ad6644b37b3e569ca3de8c0f60b /drivers/net/tun.c | |
| parent | 6f7c156c08d5eaa9fff2bd062f0a2b9d09a1e7a9 (diff) | |
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 <jasowang@redhat.com>
Signed-off-by: Amos Kong <akong@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'drivers/net/tun.c')
| -rw-r--r-- | drivers/net/tun.c | 6 |
1 files 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; } |