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authorDenys Vlasenko <vda.linux@googlemail.com>2010-01-17 01:51:33 (GMT)
committer Denys Vlasenko <vda.linux@googlemail.com>2010-01-17 01:51:33 (GMT)
commit9b20adca4b2b59c791b4b5579857e4f028a969ed (patch)
treeb77738b270eb05f845213299a517929dc93b6b9f
parent5b9a910749176cabcd6e822ca46af66a9947d032 (diff)
downloadbusybox-9b20adca4b2b59c791b4b5579857e4f028a969ed.tar.gz
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ntpd: add anti-clock-hopping code
function old new delta select_and_cluster 837 950 +113 update_local_clock 759 767 +8 root_distance 61 - -61 Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
-rw-r--r--networking/ntpd.c78
1 files changed, 61 insertions, 17 deletions
diff --git a/networking/ntpd.c b/networking/ntpd.c
index b2cd0a3..aca79c9 100644
--- a/networking/ntpd.c
+++ b/networking/ntpd.c
@@ -306,13 +306,15 @@ struct globals {
uint8_t poll_exp; // s.poll
int polladj_count; // c.count
long kernel_freq_drift;
+ peer_t *last_update_peer;
double last_update_offset; // c.last
double last_update_recv_time; // s.t
double discipline_jitter; // c.jitter
-//TODO: add s.jitter - grep for it here and see clock_combine() in doc
+ //double cluster_offset; // s.offset
+ //double cluster_jitter; // s.jitter
#if !USING_KERNEL_PLL_LOOP
double discipline_freq_drift; // c.freq
-//TODO: conditionally calculate wander? it's used only for logging
+ /* Maybe conditionally calculate wander? it's used only for logging */
double discipline_wander; // c.wander
#endif
};
@@ -821,6 +823,7 @@ typedef struct {
peer_t *p;
int type;
double edge;
+ double opt_rd; /* optimization */
} point_t;
static int
compare_point_edge(const void *aa, const void *bb)
@@ -876,6 +879,7 @@ fit(peer_t *p, double rd)
static peer_t*
select_and_cluster(void)
{
+ peer_t *p;
llist_t *item;
int i, j;
int size = 3 * G.peer_cnt;
@@ -893,10 +897,11 @@ select_and_cluster(void)
num_points = 0;
item = G.ntp_peers;
if (G.initial_poll_complete) while (item != NULL) {
- peer_t *p = (peer_t *) item->data;
- double rd = root_distance(p);
- double offset = p->filter_offset;
+ double rd, offset;
+ p = (peer_t *) item->data;
+ rd = root_distance(p);
+ offset = p->filter_offset;
if (!fit(p, rd)) {
item = item->link;
continue;
@@ -911,14 +916,17 @@ select_and_cluster(void)
point[num_points].p = p;
point[num_points].type = -1;
point[num_points].edge = offset - rd;
+ point[num_points].opt_rd = rd;
num_points++;
point[num_points].p = p;
point[num_points].type = 0;
point[num_points].edge = offset;
+ point[num_points].opt_rd = rd;
num_points++;
point[num_points].p = p;
point[num_points].type = 1;
point[num_points].edge = offset + rd;
+ point[num_points].opt_rd = rd;
num_points++;
item = item->link;
}
@@ -999,14 +1007,12 @@ select_and_cluster(void)
*/
num_survivors = 0;
for (i = 0; i < num_points; i++) {
- peer_t *p;
-
if (point[i].edge < low || point[i].edge > high)
continue;
p = point[i].p;
survivor[num_survivors].p = p;
-//TODO: save root_distance in point_t and reuse here?
- survivor[num_survivors].metric = MAXDIST * p->lastpkt_stratum + root_distance(p);
+ /* x.opt_rd == root_distance(p); */
+ survivor[num_survivors].metric = MAXDIST * p->lastpkt_stratum + point[i].opt_rd;
VERB4 bb_error_msg("survivor[%d] metric:%f peer:%s",
num_survivors, survivor[num_survivors].metric, p->p_dotted);
num_survivors++;
@@ -1050,8 +1056,8 @@ select_and_cluster(void)
*/
for (i = 0; i < num_survivors; i++) {
double selection_jitter_sq;
- peer_t *p = survivor[i].p;
+ p = survivor[i].p;
if (i == 0 || p->filter_jitter < min_jitter)
min_jitter = p->filter_jitter;
@@ -1093,18 +1099,54 @@ select_and_cluster(void)
}
}
+ if (0) {
+ /* Combine the offsets of the clustering algorithm survivors
+ * using a weighted average with weight determined by the root
+ * distance. Compute the selection jitter as the weighted RMS
+ * difference between the first survivor and the remaining
+ * survivors. In some cases the inherent clock jitter can be
+ * reduced by not using this algorithm, especially when frequent
+ * clockhopping is involved. bbox: thus we don't do it.
+ */
+ double x, y, z, w;
+ y = z = w = 0;
+ for (i = 0; i < num_survivors; i++) {
+ p = survivor[i].p;
+ x = root_distance(p);
+ y += 1 / x;
+ z += p->filter_offset / x;
+ w += SQUARE(p->filter_offset - survivor[0].p->filter_offset) / x;
+ }
+ //G.cluster_offset = z / y;
+ //G.cluster_jitter = SQRT(w / y);
+ }
+
/* Pick the best clock. If the old system peer is on the list
* and at the same stratum as the first survivor on the list,
* then don't do a clock hop. Otherwise, select the first
* survivor on the list as the new system peer.
*/
-//TODO - see clock_combine()
+ p = survivor[0].p;
+ if (G.last_update_peer
+ && G.last_update_peer->lastpkt_stratum <= p->lastpkt_stratum
+ ) {
+ /* Starting from 1 is ok here */
+ for (i = 1; i < num_survivors; i++) {
+ if (G.last_update_peer == survivor[i].p) {
+ VERB4 bb_error_msg("keeping old synced peer");
+ p = G.last_update_peer;
+ goto keep_old;
+ }
+ }
+ }
+ G.last_update_peer = p;
+ keep_old:
VERB3 bb_error_msg("selected peer %s filter_offset:%f age:%f",
- survivor[0].p->p_dotted,
- survivor[0].p->filter_offset,
- G.cur_time - survivor[0].p->lastpkt_recv_time
+ p->p_dotted,
+ p->filter_offset,
+ G.cur_time - p->lastpkt_recv_time
);
- return survivor[0].p;
+ return p;
}
@@ -1131,6 +1173,7 @@ update_local_clock(peer_t *p)
int rc;
long old_tmx_offset;
struct timex tmx;
+ /* Note: can use G.cluster_offset instead: */
double offset = p->filter_offset;
double recv_time = p->lastpkt_recv_time;
double abs_offset;
@@ -1343,7 +1386,7 @@ update_local_clock(peer_t *p)
G.ntp_status = p->lastpkt_status;
G.refid = p->lastpkt_refid;
G.rootdelay = p->lastpkt_rootdelay + p->lastpkt_delay;
- dtemp = p->filter_jitter; // SQRT(SQUARE(p->filter_jitter) + SQUARE(s.jitter));
+ dtemp = p->filter_jitter; // SQRT(SQUARE(p->filter_jitter) + SQUARE(G.cluster_jitter));
dtemp += MAXD(p->filter_dispersion + FREQ_TOLERANCE * (G.cur_time - p->lastpkt_recv_time) + abs_offset, MINDISP);
G.rootdisp = p->lastpkt_rootdisp + dtemp;
VERB3 bb_error_msg("updating leap/refid/reftime/rootdisp from peer %s", p->p_dotted);
@@ -1433,7 +1476,8 @@ update_local_clock(peer_t *p)
}
#endif
G.kernel_freq_drift = tmx.freq / 65536;
- VERB2 bb_error_msg("update offset:%f, clock drift:%ld ppm", G.last_update_offset, G.kernel_freq_drift);
+ VERB2 bb_error_msg("update peer:%s, offset:%f, clock drift:%ld ppm",
+ p->p_dotted, G.last_update_offset, G.kernel_freq_drift);
return 1; /* "ok to increase poll interval" */
}