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@xxxxxxxxxx>
Signed-off-by: Amos Kong <akong@xxxxxxxxxx>
---
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 74e9405..95dbff4 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;
}
--
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