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ntpd: add anti-clock-hopping code

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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>
This commit is contained in:
Denys Vlasenko 2010-01-17 02:51:33 +01:00
parent 5b9a910749
commit 9b20adca4b
1 changed files with 61 additions and 17 deletions
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78
networking/ntpd.c
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@ -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" */
}