[PATCH bpf] Revert "xsk: Do not sleep in poll() when need_wakeup set"

From: Magnus Karlsson <magnus.karlsson@intel.com>

This reverts commit bd0687c18e635b63233dc87f38058cd728802ab4.

This patch causes a Tx only workload to go to sleep even when it does
not have to, leading to misserable performance in skb mode. It fixed
one rare problem but created a much worse one, so this need to be
reverted while I try to craft a proper solution to the original
problem.

Fixes: bd0687c18e63 ("xsk: Do not sleep in poll() when need_wakeup set")
Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
---
 net/xdp/xsk.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index 7a466ea962c5..f16074eb53c7 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c

@@ -677,6 +677,8 @@ static __poll_t xsk_poll(struct file *file, struct socket *sock,
 	struct xdp_sock *xs = xdp_sk(sk);
 	struct xsk_buff_pool *pool;
 
+	sock_poll_wait(file, sock, wait);
+
 	if (unlikely(!xsk_is_bound(xs)))
 		return mask;
 

@@ -688,8 +690,6 @@ static __poll_t xsk_poll(struct file *file, struct socket *sock,
 		else
 			/* Poll needs to drive Tx also in copy mode */
 			__xsk_sendmsg(sk);
-	} else {
-		sock_poll_wait(file, sock, wait);
 	}
 
 	if (xs->rx && !xskq_prod_is_empty(xs->rx))

base-commit: 0c3e2474605581375d808bb3b9ce0927ed3eef70
-- 
2.34.1

Hello:

This patch was applied to bpf/bpf.git (master)
by Daniel Borkmann [off-list ref]:

On Fri, 17 Dec 2021 15:56:46 +0100 you wrote:

From: Magnus Karlsson <magnus.karlsson@intel.com>

This reverts commit bd0687c18e635b63233dc87f38058cd728802ab4.

This patch causes a Tx only workload to go to sleep even when it does
not have to, leading to misserable performance in skb mode. It fixed
one rare problem but created a much worse one, so this need to be
reverted while I try to craft a proper solution to the original
problem.

[...]

Here is the summary with links:
  - [bpf] Revert "xsk: Do not sleep in poll() when need_wakeup set"
    https://git.kernel.org/bpf/bpf/c/0706a78f31c4

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