* [PATCH net] tuntap: try not batch packets for devmap
@ 2018-02-14 3:36 Jason Wang
2018-02-14 12:54 ` Michael S. Tsirkin
0 siblings, 1 reply; 2+ messages in thread
From: Jason Wang @ 2018-02-14 3:36 UTC (permalink / raw)
To: netdev, linux-kernel; +Cc: mst, christoffer.dall, Jason Wang
Commit 762c330d670e ("tuntap: add missing xdp flush") tries to fix the
devmap stall caused by missed xdp flush by counting the pending xdp
redirected packets and flush when it exceeds NAPI_POLL_WEIGHT or
MSG_MORE is clear. This may lead BUG() since xdp_do_flush() was
called under process context with preemption enabled. Simply disable
preemption may silent the warning but be not enough since process may
move between different CPUS during a batch which cause xdp_do_flush()
misses some CPU where the process run previously. For -net, fix this
by simply calling xdp_do_flush() immediately after xdp_do_redirect(),
a side effect is that this removes any possibility of batching which
could be addressed in the future.
Reported-by: Christoffer Dall <christoffer.dall@linaro.org>
Fixes: 762c330d670e ("tuntap: add missing xdp flush")
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
drivers/net/tun.c | 15 +--------------
1 file changed, 1 insertion(+), 14 deletions(-)
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 17e496b..6a4cd97 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -181,7 +181,6 @@ struct tun_file {
struct tun_struct *detached;
struct ptr_ring tx_ring;
struct xdp_rxq_info xdp_rxq;
- int xdp_pending_pkts;
};
struct tun_flow_entry {
@@ -1666,10 +1665,10 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
case XDP_REDIRECT:
get_page(alloc_frag->page);
alloc_frag->offset += buflen;
- ++tfile->xdp_pending_pkts;
err = xdp_do_redirect(tun->dev, &xdp, xdp_prog);
if (err)
goto err_redirect;
+ xdp_do_flush_map();
rcu_read_unlock();
return NULL;
case XDP_TX:
@@ -1988,11 +1987,6 @@ static ssize_t tun_chr_write_iter(struct kiocb *iocb, struct iov_iter *from)
result = tun_get_user(tun, tfile, NULL, from,
file->f_flags & O_NONBLOCK, false);
- if (tfile->xdp_pending_pkts) {
- tfile->xdp_pending_pkts = 0;
- xdp_do_flush_map();
- }
-
tun_put(tun);
return result;
}
@@ -2330,12 +2324,6 @@ static int tun_sendmsg(struct socket *sock, struct msghdr *m, size_t total_len)
m->msg_flags & MSG_DONTWAIT,
m->msg_flags & MSG_MORE);
- if (tfile->xdp_pending_pkts >= NAPI_POLL_WEIGHT ||
- !(m->msg_flags & MSG_MORE)) {
- tfile->xdp_pending_pkts = 0;
- xdp_do_flush_map();
- }
-
tun_put(tun);
return ret;
}
@@ -3167,7 +3155,6 @@ static int tun_chr_open(struct inode *inode, struct file * file)
sock_set_flag(&tfile->sk, SOCK_ZEROCOPY);
memset(&tfile->tx_ring, 0, sizeof(tfile->tx_ring));
- tfile->xdp_pending_pkts = 0;
return 0;
}
--
2.7.4
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH net] tuntap: try not batch packets for devmap
2018-02-14 3:36 [PATCH net] tuntap: try not batch packets for devmap Jason Wang
@ 2018-02-14 12:54 ` Michael S. Tsirkin
0 siblings, 0 replies; 2+ messages in thread
From: Michael S. Tsirkin @ 2018-02-14 12:54 UTC (permalink / raw)
To: Jason Wang; +Cc: netdev, linux-kernel, christoffer.dall
On Wed, Feb 14, 2018 at 11:36:05AM +0800, Jason Wang wrote:
> Commit 762c330d670e ("tuntap: add missing xdp flush") tries to fix the
> devmap stall caused by missed xdp flush by counting the pending xdp
> redirected packets and flush when it exceeds NAPI_POLL_WEIGHT or
> MSG_MORE is clear. This may lead BUG() since xdp_do_flush() was
> called under process context with preemption enabled. Simply disable
> preemption may silent the warning but be not enough since process may
> move between different CPUS during a batch which cause xdp_do_flush()
> misses some CPU where the process run previously. For -net, fix this
> by simply calling xdp_do_flush() immediately after xdp_do_redirect(),
> a side effect is that this removes any possibility of batching which
> could be addressed in the future.
>
> Reported-by: Christoffer Dall <christoffer.dall@linaro.org>
> Fixes: 762c330d670e ("tuntap: add missing xdp flush")
Much of that patch is reverted here. How about a revert
followed by a one-liner calling xdp_do_redirect?
Will make backporting easier for people.
> Signed-off-by: Jason Wang <jasowang@redhat.com>
change itself is fine, feel free to include my
Acked-by: Michael S. Tsirkin <mst@redhat.com>
> ---
> drivers/net/tun.c | 15 +--------------
> 1 file changed, 1 insertion(+), 14 deletions(-)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 17e496b..6a4cd97 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -181,7 +181,6 @@ struct tun_file {
> struct tun_struct *detached;
> struct ptr_ring tx_ring;
> struct xdp_rxq_info xdp_rxq;
> - int xdp_pending_pkts;
> };
>
> struct tun_flow_entry {
> @@ -1666,10 +1665,10 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
> case XDP_REDIRECT:
> get_page(alloc_frag->page);
> alloc_frag->offset += buflen;
> - ++tfile->xdp_pending_pkts;
> err = xdp_do_redirect(tun->dev, &xdp, xdp_prog);
> if (err)
> goto err_redirect;
> + xdp_do_flush_map();
> rcu_read_unlock();
> return NULL;
> case XDP_TX:
> @@ -1988,11 +1987,6 @@ static ssize_t tun_chr_write_iter(struct kiocb *iocb, struct iov_iter *from)
> result = tun_get_user(tun, tfile, NULL, from,
> file->f_flags & O_NONBLOCK, false);
>
> - if (tfile->xdp_pending_pkts) {
> - tfile->xdp_pending_pkts = 0;
> - xdp_do_flush_map();
> - }
> -
> tun_put(tun);
> return result;
> }
> @@ -2330,12 +2324,6 @@ static int tun_sendmsg(struct socket *sock, struct msghdr *m, size_t total_len)
> m->msg_flags & MSG_DONTWAIT,
> m->msg_flags & MSG_MORE);
>
> - if (tfile->xdp_pending_pkts >= NAPI_POLL_WEIGHT ||
> - !(m->msg_flags & MSG_MORE)) {
> - tfile->xdp_pending_pkts = 0;
> - xdp_do_flush_map();
> - }
> -
> tun_put(tun);
> return ret;
> }
> @@ -3167,7 +3155,6 @@ static int tun_chr_open(struct inode *inode, struct file * file)
> sock_set_flag(&tfile->sk, SOCK_ZEROCOPY);
>
> memset(&tfile->tx_ring, 0, sizeof(tfile->tx_ring));
> - tfile->xdp_pending_pkts = 0;
>
> return 0;
> }
> --
> 2.7.4
^ permalink raw reply [flat|nested] 2+ messages in thread
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2018-02-14 12:54 ` Michael S. Tsirkin
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