[PATCH bpf-next v4 05/10] xsk: add busy-poll support for {recv,send}msg()

[Björn Töpel]

From: Björn Töpel <bjorn.to...@intel.com>

Wire-up XDP socket busy-poll support for recvmsg() and sendmsg(). If
the XDP socket prefers busy-polling, make sure that no wakeup/IPI is
performed.

Acked-by: Magnus Karlsson <magnus.karls...@intel.com>
Signed-off-by: Björn Töpel <bjorn.to...@intel.com>
---
 net/xdp/xsk.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index c72b4dba2878..a8501a5477cf 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -23,6 +23,7 @@
 #include <linux/netdevice.h>
 #include <linux/rculist.h>
 #include <net/xdp_sock_drv.h>
+#include <net/busy_poll.h>
 #include <net/xdp.h>
 
 #include "xsk_queue.h"
@@ -517,6 +518,17 @@ static int __xsk_sendmsg(struct sock *sk)
        return xs->zc ? xsk_zc_xmit(xs) : xsk_generic_xmit(sk);
 }
 
+static bool xsk_no_wakeup(struct sock *sk)
+{
+#ifdef CONFIG_NET_RX_BUSY_POLL
+       /* Prefer busy-polling, skip the wakeup. */
+       return READ_ONCE(sk->sk_prefer_busy_poll) && READ_ONCE(sk->sk_ll_usec) 
&&
+               READ_ONCE(sk->sk_napi_id) >= MIN_NAPI_ID;
+#else
+       return false;
+#endif
+}
+
 static int xsk_sendmsg(struct socket *sock, struct msghdr *m, size_t total_len)
 {
        bool need_wait = !(m->msg_flags & MSG_DONTWAIT);
@@ -529,6 +541,12 @@ static int xsk_sendmsg(struct socket *sock, struct msghdr 
*m, size_t total_len)
        if (unlikely(need_wait))
                return -EOPNOTSUPP;
 
+       if (sk_can_busy_loop(sk))
+               sk_busy_loop(sk, 1); /* only support non-blocking sockets */
+
+       if (xsk_no_wakeup(sk))
+               return 0;
+
        pool = xs->pool;
        if (pool->cached_need_wakeup & XDP_WAKEUP_TX)
                return __xsk_sendmsg(sk);
@@ -550,6 +568,12 @@ static int xsk_recvmsg(struct socket *sock, struct msghdr 
*m, size_t len, int fl
        if (unlikely(need_wait))
                return -EOPNOTSUPP;
 
+       if (sk_can_busy_loop(sk))
+               sk_busy_loop(sk, 1); /* only support non-blocking sockets */
+
+       if (xsk_no_wakeup(sk))
+               return 0;
+
        if (xs->pool->cached_need_wakeup & XDP_WAKEUP_RX && xs->zc)
                return xsk_wakeup(xs, XDP_WAKEUP_RX);
        return 0;
-- 
2.27.0