[PATCH net] net: busy-poll: use ktime_get_ns() instead of local_clock()

[Eric Dumazet <edumazet@google.com>]

Typically, busy-polling durations are below 100 usec.

When/if the busy-poller thread migrates to another cpu,
local_clock() can be off by +/-2msec or more for small
values of HZ, depending on the platform.

Use ktimer_get_ns() to ensure deterministic behavior,
which is the whole point of busy-polling.

Fixes: 060212928670 ("net: add low latency socket poll")
Fixes: 9a3c71aa8024 ("net: convert low latency sockets to sched_clock()")
Fixes: 37089834528b ("sched, net: Fixup busy_loop_us_clock()")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Joe Damato <jdamato@fastly.com>
---
 include/net/busy_poll.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/net/busy_poll.h b/include/net/busy_poll.h
index 9b09acac538eed8dbaa2576bf2af926ecd98eb44..522f1da8b747ac73578d8fd93301d31835a6dae0 100644
--- a/include/net/busy_poll.h
+++ b/include/net/busy_poll.h
@@ -68,7 +68,7 @@ static inline bool sk_can_busy_loop(struct sock *sk)
 static inline unsigned long busy_loop_current_time(void)
 {
 #ifdef CONFIG_NET_RX_BUSY_POLL
-	return (unsigned long)(local_clock() >> 10);
+	return (unsigned long)(ktime_get_ns() >> 10);
 #else
 	return 0;
 #endif
-- 
2.46.0.295.g3b9ea8a38a-goog