From: Jakub Kicinski <jakub.kicinski@netronome.com>
Date: Wed, 17 Jan 2018 19:13:32 -0800
Subject: nfp: bpf: add short busy wait for FW replies
Patch-mainline: v4.16-rc1
Git-commit: ca027a1c45e30d89c5cc6dcacbdcea74e1ff65fc
References: bsc#1109837

Scheduling out and in for every FW message can slow us down
unnecessarily.  Our experiments show that even under heavy load
the FW responds to 99.9% messages within 200 us.  Add a short
busy wait before entering the wait queue.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 drivers/net/ethernet/netronome/nfp/bpf/cmsg.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

--- a/drivers/net/ethernet/netronome/nfp/bpf/cmsg.c
+++ b/drivers/net/ethernet/netronome/nfp/bpf/cmsg.c
@@ -157,7 +157,14 @@ nfp_bpf_cmsg_wait_reply(struct nfp_app_b
 			int tag)
 {
 	struct sk_buff *skb;
-	int err;
+	int i, err;
+
+	for (i = 0; i < 50; i++) {
+		udelay(4);
+		skb = nfp_bpf_reply(bpf, tag);
+		if (skb)
+			return skb;
+	}
 
 	err = wait_event_interruptible_timeout(bpf->cmsg_wq,
 					       skb = nfp_bpf_reply(bpf, tag),