[PATCH net-next 2/2] tuntap: free XDP dropped packets in a batch

Jason Wang
2018-11-15T09:43:10Z

Thanks to the batched XDP buffs through msg_control. Instead of
calling put_page() for each page which involves a atomic operation,
let's batch them by record the last page that needs to be freed and
its refcnt count and free them in a batch.

Testpmd(virtio-user + vhost_net) + XDP_DROP shows 3.8% improvement.

Before: 4.71Mpps
After : 4.89Mpps

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
drivers/net/tun.c | 29 ++++++++++++++++++++++++++---
1 file changed, 26 insertions(+), 3 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index a65779c6d72f..e90a7923a5f6 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -188,6 +188,11 @@ struct tun_file {
struct xdp_rxq_info xdp_rxq;
};

+struct tun_page {
+ struct page *page;
+ int count;
+};
+
struct tun_flow_entry {
struct hlist_node hash_link;
struct rcu_head rcu;
@@ -2377,9 +2382,16 @@ static void tun_sock_write_space(struct sock *sk)
kill_fasync(&tfile->fasync, SIGIO, POLL_OUT);
}

+static void tun_put_page(struct tun_page *tpage)
+{
+ if (tpage->page)
+ __page_frag_cache_drain(tpage->page, tpage->count);
+}
+
static int tun_xdp_one(struct tun_struct *tun,
struct tun_file *tfile,
- struct xdp_buff *xdp, int *flush)
+ struct xdp_buff *xdp, int *flush,
+ struct tun_page *tpage)
{
struct tun_xdp_hdr *hdr = xdp->data_hard_start;
struct virtio_net_hdr *gso = &hdr->gso;
@@ -2390,6 +2402,7 @@ static int tun_xdp_one(struct tun_struct *tun,
int buflen = hdr->buflen;
int err = 0;
bool skb_xdp = false;
+ struct page *page;

xdp_prog = rcu_dereference(tun->xdp_prog);
if (xdp_prog) {
@@ -2416,7 +2429,14 @@ static int tun_xdp_one(struct tun_struct *tun,
case XDP_PASS:
break;
default:
- put_page(virt_to_head_page(xdp->data));
+ page = virt_to_head_page(xdp->data);
+ if (tpage->page == page) {
+ ++tpage->count;
+ } else {
+ tun_put_page(tpage);
+ tpage->page = page;
+ tpage->count = 1;
+ }
return 0;
}
}
@@ -2480,6 +2500,7 @@ static int tun_sendmsg(struct socket *sock, struct msghdr *m, size_t total_len)
return -EBADFD;

if (ctl && (ctl->type == TUN_MSG_PTR)) {
+ struct tun_page tpage = {0};
int n = ctl->num;
int flush = 0;

@@ -2488,7 +2509,7 @@ static int tun_sendmsg(struct socket *sock, struct msghdr *m, size_t total_len)

for (i = 0; i < n; i++) {
xdp = &((struct xdp_buff *)ctl->ptr)[i];
- tun_xdp_one(tun, tfile, xdp, &flush);
+ tun_xdp_one(tun, tfile, xdp, &flush, &tpage);
}

if (flush)
@@ -2497,6 +2518,8 @@ static int tun_sendmsg(struct socket *sock, struct msghdr *m, size_t total_len)
rcu_read_unlock();
local_bh_enable();

+ tun_put_page(&tpage);
+
ret = total_len;
goto out;
}
--
2.17.1