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Implement DL_SCHED_RANDOM_EXPONENTIAL support for download_status_t

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This commit is contained in:
Andrea Shepard 2016-06-12 19:07:11 +00:00
parent 033cf30b3c
commit 695b0bd1d5
5 changed files with 130 additions and 13 deletions
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112
src/or/directory.c
View File

@ -3762,6 +3762,28 @@ find_dl_schedule(download_status_t *dls, const or_options_t *options)
return NULL;
}
/** Decide which minimum and maximum delay step we want to use based on
* descriptor type in <b>dls</b> and <b>options</b>.
* Helper function for download_status_schedule_get_delay(). */
STATIC void
find_dl_min_and_max_delay(download_status_t *dls, const or_options_t *options,
int *min, int *max)
{
tor_assert(dls);
tor_assert(options);
tor_assert(min);
tor_assert(max);
/*
* For now, just use the existing schedule config stuff and pick the
* first/last entries off to get min/max delay for backoff purposes
*/
const smartlist_t *schedule = find_dl_schedule(dls, options);
tor_assert(schedule != NULL && smartlist_len(schedule) >= 2);
*min = *((int *)(smartlist_get(schedule, 0)));
*max = *((int *)((smartlist_get(schedule, smartlist_len(schedule) - 1))));
}
/* Find the current delay for dls based on schedule.
* Set dls->next_attempt_at based on now, and return the delay.
* Helper for download_status_increment_failure and
@ -3769,23 +3791,85 @@ find_dl_schedule(download_status_t *dls, const or_options_t *options)
STATIC int
download_status_schedule_get_delay(download_status_t *dls,
const smartlist_t *schedule,
int min_delay, int max_delay,
time_t now)
{
tor_assert(dls);
tor_assert(schedule);
/* We don't need a schedule if we're using random exponential backoff */
tor_assert(dls->backoff == DL_SCHED_RANDOM_EXPONENTIAL ||
schedule != NULL);
/* If we're using random exponential backoff, we do need min/max delay */
tor_assert(dls->backoff != DL_SCHED_RANDOM_EXPONENTIAL ||
(min_delay >= 0 && max_delay >= min_delay &&
max_delay <= INT_MAX));
int delay = INT_MAX;
int delay_increment, i;
uint8_t dls_schedule_position = (dls->increment_on
== DL_SCHED_INCREMENT_ATTEMPT
? dls->n_download_attempts
: dls->n_download_failures);
uint8_t entropy;
if (dls_schedule_position < smartlist_len(schedule))
delay = *(int *)smartlist_get(schedule, dls_schedule_position);
else if (dls_schedule_position == IMPOSSIBLE_TO_DOWNLOAD)
delay = INT_MAX;
else
delay = *(int *)smartlist_get(schedule, smartlist_len(schedule) - 1);
if (dls->backoff == DL_SCHED_DETERMINISTIC) {
if (dls_schedule_position < smartlist_len(schedule))
delay = *(int *)smartlist_get(schedule, dls_schedule_position);
else if (dls_schedule_position == IMPOSSIBLE_TO_DOWNLOAD)
delay = INT_MAX;
else
delay = *(int *)smartlist_get(schedule, smartlist_len(schedule) - 1);
} else if (dls->backoff == DL_SCHED_RANDOM_EXPONENTIAL) {
/* Check if we missed a reset somehow */
if (dls->last_backoff_position > dls_schedule_position) {
dls->last_backoff_position = 0;
dls->last_delay_used = 0;
}
if (dls_schedule_position > 0) {
delay = dls->last_delay_used;
while (dls->last_backoff_position < dls_schedule_position) {
/*
* Backoff step: we want to multiply by something ~1.5, and then add
* 1 with non-zero probability so we can't get stuck at zero even if
* we start out with zero delay. To do this, pick a uint8_t of
* entropy in the range [0,255], and use it to construct an
* increment.
*/
delay_increment = 0;
/* Get a byte of entropy */
crypto_rand((char *)(&entropy), sizeof(entropy));
/* Clamp it just to be sure */
entropy &= 0xff;
/* If we have non-zero delay; otherwise this is a no-op */
if (delay > 0) {
/* Use the low 7 bits for the increment */
for (i = 0; i < 7; ++i) {
if (entropy & (0x1 << i)) delay_increment += (delay >> (i + 1));
}
}
/*
* Using the remaining bit of entropy, add 1 with probability 50% so
* we can't get stuck at 0
*/
if (entropy & 0x80) delay_increment += 1;
/* Increment delay, make sure to saturate if we would wrap around */
if (delay_increment < max_delay - delay) delay += delay_increment;
else delay = max_delay;
++(dls->last_backoff_position);
}
} else {
delay = min_delay;
}
/* Clamp it within min/max if we have them */
if (min_delay >= 0 && delay < min_delay) delay = min_delay;
if (max_delay != INT_MAX && delay > max_delay) delay = max_delay;
/* Store it for next time */
dls->last_backoff_position = dls_schedule_position;
dls->last_delay_used = delay;
}
/* A negative delay makes no sense. Knowing that delay is
* non-negative allows us to safely do the wrapping check below. */
@ -3846,6 +3930,8 @@ download_status_increment_failure(download_status_t *dls, int status_code,
const char *item, int server, time_t now)
{
int increment = -1;
int min_delay = 0, max_delay = INT_MAX;
tor_assert(dls);
/* only count the failure if it's permanent, or we're a server */
@ -3866,7 +3952,9 @@ download_status_increment_failure(download_status_t *dls, int status_code,
/* only return a failure retry time if this schedule increments on failures
*/
const smartlist_t *schedule = find_dl_schedule(dls, get_options());
increment = download_status_schedule_get_delay(dls, schedule, now);
find_dl_min_and_max_delay(dls, get_options(), &min_delay, &max_delay);
increment = download_status_schedule_get_delay(dls, schedule,
min_delay, max_delay, now);
}
download_status_log_helper(item, !dls->increment_on, "failed",
@ -3895,6 +3983,8 @@ download_status_increment_attempt(download_status_t *dls, const char *item,
time_t now)
{
int delay = -1;
int min_delay = 0, max_delay = INT_MAX;
tor_assert(dls);
if (dls->increment_on == DL_SCHED_INCREMENT_FAILURE) {
@ -3909,7 +3999,9 @@ download_status_increment_attempt(download_status_t *dls, const char *item,
++dls->n_download_attempts;
const smartlist_t *schedule = find_dl_schedule(dls, get_options());
delay = download_status_schedule_get_delay(dls, schedule, now);
find_dl_min_and_max_delay(dls, get_options(), &min_delay, &max_delay);
delay = download_status_schedule_get_delay(dls, schedule,
min_delay, max_delay, now);
download_status_log_helper(item, dls->increment_on, "attempted",
"on failure", dls->n_download_attempts,
@ -3941,6 +4033,8 @@ download_status_reset(download_status_t *dls)
dls->n_download_failures = 0;
dls->n_download_attempts = 0;
dls->next_attempt_at = time(NULL) + *(int *)smartlist_get(schedule, 0);
dls->last_backoff_position = 0;
dls->last_delay_used = 0;
/* Don't reset dls->want_authority or dls->increment_on */
}

4
src/or/directory.h
View File

@ -146,6 +146,7 @@ STATIC int directory_handle_command_get(dir_connection_t *conn,
size_t req_body_len);
STATIC int download_status_schedule_get_delay(download_status_t *dls,
const smartlist_t *schedule,
int min_delay, int max_delay,
time_t now);
STATIC char* authdir_type_to_string(dirinfo_type_t auth);
@ -154,6 +155,9 @@ STATIC int should_use_directory_guards(const or_options_t *options);
STATIC zlib_compression_level_t choose_compression_level(ssize_t n_bytes);
STATIC const smartlist_t *find_dl_schedule(download_status_t *dls,
const or_options_t *options);
STATIC void find_dl_min_and_max_delay(download_status_t *dls,
const or_options_t *options,
int *min, int *max);
#endif
#endif

8
src/or/networkstatus.c
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@ -86,9 +86,9 @@ static time_t time_to_download_next_consensus[N_CONSENSUS_FLAVORS];
static download_status_t consensus_dl_status[N_CONSENSUS_FLAVORS] =
{
{ 0, 0, 0, DL_SCHED_CONSENSUS, DL_WANT_ANY_DIRSERVER,
DL_SCHED_INCREMENT_FAILURE },
DL_SCHED_INCREMENT_FAILURE, DL_SCHED_DETERMINISTIC, 0, 0 },
{ 0, 0, 0, DL_SCHED_CONSENSUS, DL_WANT_ANY_DIRSERVER,
DL_SCHED_INCREMENT_FAILURE },
DL_SCHED_INCREMENT_FAILURE, DL_SCHED_DETERMINISTIC, 0, 0 },
};
#define N_CONSENSUS_BOOTSTRAP_SCHEDULES 2
@ -105,10 +105,10 @@ static download_status_t
consensus_bootstrap_dl_status[N_CONSENSUS_BOOTSTRAP_SCHEDULES] =
{
{ 0, 0, 0, DL_SCHED_CONSENSUS, DL_WANT_AUTHORITY,
DL_SCHED_INCREMENT_ATTEMPT },
DL_SCHED_INCREMENT_ATTEMPT, DL_SCHED_DETERMINISTIC, 0, 0 },
/* During bootstrap, DL_WANT_ANY_DIRSERVER means "use fallbacks". */
{ 0, 0, 0, DL_SCHED_CONSENSUS, DL_WANT_ANY_DIRSERVER,
DL_SCHED_INCREMENT_ATTEMPT },
DL_SCHED_INCREMENT_ATTEMPT, DL_SCHED_DETERMINISTIC, 0, 0 },
};
/** True iff we have logged a warning about this OR's version being older than

16
src/or/or.h
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@ -1987,6 +1987,15 @@ typedef enum {
#define download_schedule_increment_bitfield_t \
ENUM_BF(download_schedule_increment_t)
/** Enumeration: do we want to use the random exponential backoff
* mechanism? */
typedef enum {
DL_SCHED_DETERMINISTIC = 0,
DL_SCHED_RANDOM_EXPONENTIAL = 1,
} download_schedule_backoff_t;
#define download_schedule_backoff_bitfield_t \
ENUM_BF(download_schedule_backoff_t)
/** Information about our plans for retrying downloads for a downloadable
* directory object.
* Each type of downloadable directory object has a corresponding retry
@ -2033,6 +2042,13 @@ typedef struct download_status_t {
download_schedule_increment_bitfield_t increment_on : 1; /**< does this
* schedule increment on each attempt,
* or after each failure? */
download_schedule_backoff_bitfield_t backoff : 1; /**< do we use the
* deterministic schedule, or random
* exponential backoffs? */
uint8_t last_backoff_position; /**< number of attempts/failures, depending
* on increment_on, when we last recalculated
* the delay. */
int last_delay_used; /**< last delay used for random exponential backoff */
} download_status_t;
/** If n_download_failures is this high, the download can never happen. */

3
src/or/routerlist.c
View File

@ -159,6 +159,9 @@ download_status_cert_init(download_status_t *dlstatus)
dlstatus->schedule = DL_SCHED_CONSENSUS;
dlstatus->want_authority = DL_WANT_ANY_DIRSERVER;
dlstatus->increment_on = DL_SCHED_INCREMENT_FAILURE;
dlstatus->backoff = DL_SCHED_DETERMINISTIC;
dlstatus->last_backoff_position = 0;
dlstatus->last_delay_used = 0;
/* Use the new schedule to set next_attempt_at */
download_status_reset(dlstatus);