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authorLinus Torvalds <torvalds@linux-foundation.org>2010-10-21 14:08:08 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2010-10-21 14:08:08 -0700
commit62bea97f54d806218a992b18d1f425cfb5060175 (patch)
tree56269aab888af586f4f63ed6a05286d11e46168c /kernel
parentb61f6a57f1919ef8dbd33f864df9b8b361c65b11 (diff)
parent8af3c153baf95374eff20a37f00c59a295b52756 (diff)
Merge branch 'timers-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
* 'timers-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: ntp: Clamp PLL update interval
Diffstat (limited to 'kernel')
-rw-r--r--kernel/time/ntp.c14
1 files changed, 11 insertions, 3 deletions
diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
index c63116863a80..d2321891538f 100644
--- a/kernel/time/ntp.c
+++ b/kernel/time/ntp.c
@@ -149,10 +149,18 @@ static void ntp_update_offset(long offset)
time_reftime = get_seconds();
offset64 = offset;
- freq_adj = (offset64 * secs) <<
- (NTP_SCALE_SHIFT - 2 * (SHIFT_PLL + 2 + time_constant));
+ freq_adj = ntp_update_offset_fll(offset64, secs);
- freq_adj += ntp_update_offset_fll(offset64, secs);
+ /*
+ * Clamp update interval to reduce PLL gain with low
+ * sampling rate (e.g. intermittent network connection)
+ * to avoid instability.
+ */
+ if (unlikely(secs > 1 << (SHIFT_PLL + 1 + time_constant)))
+ secs = 1 << (SHIFT_PLL + 1 + time_constant);
+
+ freq_adj += (offset64 * secs) <<
+ (NTP_SCALE_SHIFT - 2 * (SHIFT_PLL + 2 + time_constant));
freq_adj = min(freq_adj + time_freq, MAXFREQ_SCALED);