[git commit] ntpd: decrease MIN_FREQHOLD by 2, increase "penalty" for largish offset x2

[Denys Vlasenko]

commit: https://git.busybox.net/busybox/commit/?id=ea096d6c1389c93bdb6c6c45a04aff9062c7d8cf
branch: https://git.busybox.net/busybox/commit/?id=refs/heads/master

> 2018-07-25:
> ntpd: increase MIN_FREQHOLD by 3
> This means we'll start correcting frequency ~5 minutes after start,
> not ~3.5 ones.
> With previous settings I still often see largish ~0.7s initial offsets
> only about 1/2 corrected before frequency correction kicks in,
> resulting in ~200ppm "correction" which is then slowly undone.

Review of real-world results of the above shows that with small
initial offsets, freq correction can be allowed to kick in sooner,
whereas with large (~0.8s) offsets, we still start freq correction
a bit too soon.

Let's rebalance this a bit.

Signed-off-by: Denys Vlasenko <vda.linux at googlemail.com>
---
 networking/ntpd.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/networking/ntpd.c b/networking/ntpd.c
index e11160a55..0f12409f9 100644
--- a/networking/ntpd.c
+++ b/networking/ntpd.c
@@ -164,7 +164,7 @@
  */
 
 #define INITIAL_SAMPLES    4    /* how many samples do we want for init */
-#define MIN_FREQHOLD      12    /* adjust offset, but not freq in this many first adjustments */
+#define MIN_FREQHOLD      10    /* adjust offset, but not freq in this many first adjustments */
 #define BAD_DELAY_GROWTH   4    /* drop packet if its delay grew by more than this factor */
 
 #define RETRY_INTERVAL    32    /* on send/recv error, retry in N secs (need to be power of 2) */
@@ -1876,11 +1876,11 @@ update_local_clock(peer_t *p)
 //15:31:53.473 update from:<IP> offset:+0.000007 delay:0.158142 jitter:0.010922 clock drift:+9.343ppm tc:6
 //15:32:58.902 update from:<IP> offset:-0.000728 delay:0.158222 jitter:0.009454 clock drift:+9.298ppm tc:6
 			/*
-			 * This expression would choose MIN_FREQHOLD + 8 in the above example
-			 * (off_065 is +1 for each 0.065536 seconds of offset).
+			 * This expression would choose MIN_FREQHOLD + 14 in the above example
+			 * (off_032 is +1 for each 0.032768 seconds of offset).
 			 */
-			unsigned off_065 = abs((int)(tmx.offset >> 16));
-			G.FREQHOLD_cnt = 1 + MIN_FREQHOLD + off_065;
+			unsigned off_032 = abs((int)(tmx.offset >> 15));
+			G.FREQHOLD_cnt = 1 + MIN_FREQHOLD + off_032;
 		}
 		G.FREQHOLD_cnt--;
 		tmx.status |= STA_FREQHOLD;