Re: [PATCH,v3,net-next 1/2] tun: enable NAPI for TUN/TAP driver

[महेश बंडेवार]

On Fri, Sep 22, 2017 at 1:49 PM, Petar Penkov  wrote:
> Changes TUN driver to use napi_gro_receive() upon receiving packets
> rather than netif_rx_ni(). Adds flag IFF_NAPI that enables these
> changes and operation is not affected if the flag is disabled.  SKBs
> are constructed upon packet arrival and are queued to be processed
> later.
>
> The new path was evaluated with a benchmark with the following setup:
> Open two tap devices and a receiver thread that reads in a loop for
> each device. Start one sender thread and pin all threads to different
> CPUs. Send 1M minimum UDP packets to each device and measure sending
> time for each of the sending methods:
> napi_gro_receive(): 4.90s
> netif_rx_ni():  4.90s
> netif_receive_skb():7.20s
>
> Signed-off-by: Petar Penkov 

Thank you Petar.

Acked-by: Mahesh Bandewar 

> Cc: Eric Dumazet 
> Cc: Mahesh Bandewar 
> Cc: Willem de Bruijn 
> Cc: da...@davemloft.net
> Cc: ppen...@stanford.edu
> ---
>  drivers/net/tun.c   | 133 
> +++-
>  include/uapi/linux/if_tun.h |   1 +
>  2 files changed, 119 insertions(+), 15 deletions(-)
>

[PATCH,v3,net-next 1/2] tun: enable NAPI for TUN/TAP driver

[Petar Penkov]

Changes TUN driver to use napi_gro_receive() upon receiving packets
rather than netif_rx_ni(). Adds flag IFF_NAPI that enables these
changes and operation is not affected if the flag is disabled.  SKBs
are constructed upon packet arrival and are queued to be processed
later.

The new path was evaluated with a benchmark with the following setup:
Open two tap devices and a receiver thread that reads in a loop for
each device. Start one sender thread and pin all threads to different
CPUs. Send 1M minimum UDP packets to each device and measure sending
time for each of the sending methods:
napi_gro_receive(): 4.90s
netif_rx_ni():  4.90s
netif_receive_skb():7.20s

Signed-off-by: Petar Penkov 
Cc: Eric Dumazet 
Cc: Mahesh Bandewar 
Cc: Willem de Bruijn 
Cc: da...@davemloft.net
Cc: ppen...@stanford.edu
---
 drivers/net/tun.c   | 133 +++-
 include/uapi/linux/if_tun.h |   1 +
 2 files changed, 119 insertions(+), 15 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 3c9985f29950..f16407242b18 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -121,7 +121,7 @@ do {
\
 #define TUN_VNET_BE 0x4000
 
 #define TUN_FEATURES (IFF_NO_PI | IFF_ONE_QUEUE | IFF_VNET_HDR | \
- IFF_MULTI_QUEUE)
+ IFF_MULTI_QUEUE | IFF_NAPI)
 #define GOODCOPY_LEN 128
 
 #define FLT_EXACT_COUNT 8
@@ -172,6 +172,7 @@ struct tun_file {
u16 queue_index;
unsigned int ifindex;
};
+   struct napi_struct napi;
struct list_head next;
struct tun_struct *detached;
struct skb_array tx_array;
@@ -229,6 +230,68 @@ struct tun_struct {
struct bpf_prog __rcu *xdp_prog;
 };
 
+static int tun_napi_receive(struct napi_struct *napi, int budget)
+{
+   struct tun_file *tfile = container_of(napi, struct tun_file, napi);
+   struct sk_buff_head *queue = >sk.sk_write_queue;
+   struct sk_buff_head process_queue;
+   struct sk_buff *skb;
+   int received = 0;
+
+   __skb_queue_head_init(_queue);
+
+   spin_lock(>lock);
+   skb_queue_splice_tail_init(queue, _queue);
+   spin_unlock(>lock);
+
+   while (received < budget && (skb = __skb_dequeue(_queue))) {
+   napi_gro_receive(napi, skb);
+   ++received;
+   }
+
+   if (!skb_queue_empty(_queue)) {
+   spin_lock(>lock);
+   skb_queue_splice(_queue, queue);
+   spin_unlock(>lock);
+   }
+
+   return received;
+}
+
+static int tun_napi_poll(struct napi_struct *napi, int budget)
+{
+   unsigned int received;
+
+   received = tun_napi_receive(napi, budget);
+
+   if (received < budget)
+   napi_complete_done(napi, received);
+
+   return received;
+}
+
+static void tun_napi_init(struct tun_struct *tun, struct tun_file *tfile,
+ bool napi_en)
+{
+   if (napi_en) {
+   netif_napi_add(tun->dev, >napi, tun_napi_poll,
+  NAPI_POLL_WEIGHT);
+   napi_enable(>napi);
+   }
+}
+
+static void tun_napi_disable(struct tun_struct *tun, struct tun_file *tfile)
+{
+   if (tun->flags & IFF_NAPI)
+   napi_disable(>napi);
+}
+
+static void tun_napi_del(struct tun_struct *tun, struct tun_file *tfile)
+{
+   if (tun->flags & IFF_NAPI)
+   netif_napi_del(>napi);
+}
+
 #ifdef CONFIG_TUN_VNET_CROSS_LE
 static inline bool tun_legacy_is_little_endian(struct tun_struct *tun)
 {
@@ -541,6 +604,11 @@ static void __tun_detach(struct tun_file *tfile, bool 
clean)
 
tun = rtnl_dereference(tfile->tun);
 
+   if (tun && clean) {
+   tun_napi_disable(tun, tfile);
+   tun_napi_del(tun, tfile);
+   }
+
if (tun && !tfile->detached) {
u16 index = tfile->queue_index;
BUG_ON(index >= tun->numqueues);
@@ -598,6 +666,7 @@ static void tun_detach_all(struct net_device *dev)
for (i = 0; i < n; i++) {
tfile = rtnl_dereference(tun->tfiles[i]);
BUG_ON(!tfile);
+   tun_napi_disable(tun, tfile);
tfile->socket.sk->sk_shutdown = RCV_SHUTDOWN;
tfile->socket.sk->sk_data_ready(tfile->socket.sk);
RCU_INIT_POINTER(tfile->tun, NULL);
@@ -613,6 +682,7 @@ static void tun_detach_all(struct net_device *dev)
synchronize_net();
for (i = 0; i < n; i++) {
tfile = rtnl_dereference(tun->tfiles[i]);
+   tun_napi_del(tun, tfile);
/* Drop read queue */
tun_queue_purge(tfile);
sock_put(>sk);
@@ -631,7 +701,8 @@ static void tun_detach_all(struct net_device *dev)