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Eliminate some unnecessary smartlists in scheduler.c

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This commit is contained in:
Andrea Shepard 2013-12-06 00:04:12 -08:00
parent 283646fd90
commit 3530825c53
3 changed files with 70 additions and 68 deletions
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3
src/or/channel.c
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@ -806,6 +806,9 @@ channel_init(channel_t *chan)
/* It hasn't been open yet. */
chan->has_been_open = 0;
/* Scheduler state is idle */
chan->scheduler_state = SCHED_CHAN_IDLE;
}
/**

23
src/or/channel.h
View File

@ -57,6 +57,29 @@ struct channel_s {
CHANNEL_CLOSE_FOR_ERROR
} reason_for_closing;
/** State variable for use by the scheduler */
enum {
/*
* The channel is not open, or it has a full output buffer but no queued
* cells.
*/
SCHED_CHAN_IDLE = 0,
/*
* The channel has space on its output buffer to write, but no queued
* cells.
*/
SCHED_CHAN_WAITING_FOR_CELLS,
/*
* The scheduler has queued cells but no output buffer space to write.
*/
SCHED_CHAN_WAITING_TO_WRITE,
/*
* The scheduler has both queued cells and output buffer space, and is
* eligible for the scheduler loop.
*/
SCHED_CHAN_PENDING
} scheduler_state;
/** Timestamps for both cell channels and listeners */
time_t timestamp_created; /* Channel created */
time_t timestamp_active; /* Any activity */

112
src/or/scheduler.c
View File

@ -24,12 +24,13 @@
#define SCHED_Q_HIGH_WATER (2 * SCHED_Q_LOW_WATER)
/*
* Write scheduling works by keeping track of lists of channels that can
* Write scheduling works by keeping track of which channels can
* accept cells, and have cells to write. From the scheduler's perspective,
* a channel can be in four possible states:
*
* 1.) Not open for writes, no cells to send
* - Not much to do here, and the channel will appear in neither list.
* - Not much to do here, and the channel will have scheduler_state ==
* SCHED_CHAN_IDLE
* - Transitions from:
* - Open for writes/has cells by simultaneously draining all circuit
* queues and filling the output buffer.
@ -41,7 +42,8 @@
*
* 2.) Open for writes, no cells to send
* - Not much here either; this will be the state an idle but open channel
* can be expected to settle in.
* can be expected to settle in. It will have scheduler_state ==
* SCHED_CHAN_WAITING_FOR_CELLS
* - Transitions from:
* - Not open for writes/no cells by flushing some of the output
* buffer.
@ -55,6 +57,7 @@
* 3.) Not open for writes, cells to send
* - This is the state of a busy circuit limited by output bandwidth;
* cells have piled up in the circuit queues waiting to be relayed.
* The channel will have scheduler_state == SCHED_CHAN_WAITING_TO_WRITE.
* - Transitions from:
* - Not open for writes/no cells by arrival of cells on an attached
* circuit
@ -66,7 +69,8 @@
*
* 4.) Open for writes, cells to send
* - This connection is ready to relay some cells and waiting for
* the scheduler to choose it
* the scheduler to choose it. The channel will have scheduler_state ==
* SCHED_CHAN_PENDING.
* - Transitions from:
* - Not open for writes/has cells by the connection_or_flushed_some()
* path
@ -91,29 +95,11 @@
/* Scheduler global data structures */
/*
* We keep lists of channels that either have cells queued, can accept
* writes, or both (states 2, 3 and 4 above) - no explicit list of state
* 1 channels is kept, so we don't have to worry about registering new
* channels here or anything. The scheduler will learn about them when
* it needs to. We can check how many channels in state 4 in O(1), so
* the test whether we have anything to do in scheduler_run() is fast
* and there's no harm in calling it opportunistically whenever we get
* the chance.
*
* Note that it takes time O(n) to search for a channel in these smartlists
* or move one; I don't think the number of channels on a relay will be large
* enough for this to be a severe problem, but this would benefit from using
* a doubly-linked list rather than smartlist_t, together with a hash map from
* channel identifiers to pointers to list entries, so we can perform those
* operations in O(log(n)).
* We keep a list of channels that are pending - i.e, have cells to write
* and can accept them to send. The enum scheduler_state in channel_t
* is reserved for our use.
*/
/* List of channels that can write but have no cells (state 2 above) */
static smartlist_t *channels_waiting_for_cells = NULL;
/* List of channels with cells waiting to write (state 3 above) */
static smartlist_t *channels_waiting_to_write = NULL;
/* List of channels that can write and have cells (pending work) */
static smartlist_t *channels_pending = NULL;
@ -165,16 +151,6 @@ scheduler_free_all(void)
run_sched_ev = NULL;
}
if (channels_waiting_for_cells) {
smartlist_free(channels_waiting_for_cells);
channels_waiting_for_cells = NULL;
}
if (channels_waiting_to_write) {
smartlist_free(channels_waiting_to_write);
channels_waiting_to_write = NULL;
}
if (channels_pending) {
smartlist_free(channels_pending);
channels_pending = NULL;
@ -255,19 +231,18 @@ void
scheduler_channel_doesnt_want_writes(channel_t *chan)
{
tor_assert(chan);
tor_assert(channels_waiting_for_cells);
tor_assert(channels_waiting_to_write);
tor_assert(channels_pending);
/* If it's already in pending, we can put it in waiting_to_write */
if (smartlist_contains(channels_pending, chan)) {
if (chan->scheduler_state == SCHED_CHAN_PENDING) {
/*
* It's in channels_pending, so it shouldn't be in any of
* the other lists. It can't write any more, so it goes to
* channels_waiting_to_write.
*/
smartlist_remove(channels_pending, chan);
smartlist_add(channels_waiting_to_write, chan);
chan->scheduler_state = SCHED_CHAN_WAITING_TO_WRITE;
log_debug(LD_SCHED,
"Channel " U64_FORMAT " at %p went from pending "
"to waiting_to_write",
@ -278,8 +253,8 @@ scheduler_channel_doesnt_want_writes(channel_t *chan)
* either not in any of the lists (nothing to do) or it's already in
* waiting_for_cells (remove it, can't write any more).
*/
if (smartlist_contains(channels_waiting_for_cells, chan)) {
smartlist_remove(channels_waiting_for_cells, chan);
if (chan->scheduler_state == SCHED_CHAN_WAITING_FOR_CELLS) {
chan->scheduler_state = SCHED_CHAN_IDLE;
log_debug(LD_SCHED,
"Channel " U64_FORMAT " at %p left waiting_for_cells",
U64_PRINTF_ARG(chan->global_identifier), chan);
@ -295,18 +270,16 @@ scheduler_channel_has_waiting_cells(channel_t *chan)
int became_pending = 0;
tor_assert(chan);
tor_assert(channels_waiting_for_cells);
tor_assert(channels_waiting_to_write);
tor_assert(channels_pending);
/* First, check if this one also writeable */
if (smartlist_contains(channels_waiting_for_cells, chan)) {
if (chan->scheduler_state == SCHED_CHAN_WAITING_FOR_CELLS) {
/*
* It's in channels_waiting_for_cells, so it shouldn't be in any of
* the other lists. It has waiting cells now, so it goes to
* channels_pending.
*/
smartlist_remove(channels_waiting_for_cells, chan);
chan->scheduler_state = SCHED_CHAN_PENDING;
smartlist_add(channels_pending, chan);
log_debug(LD_SCHED,
"Channel " U64_FORMAT " at %p went from waiting_for_cells "
@ -319,9 +292,9 @@ scheduler_channel_has_waiting_cells(channel_t *chan)
* either not in any of the lists (we add it to waiting_to_write)
* or it's already in waiting_to_write or pending (we do nothing)
*/
if (!(smartlist_contains(channels_waiting_to_write, chan) ||
smartlist_contains(channels_pending, chan))) {
smartlist_add(channels_waiting_to_write, chan);
if (!(chan->scheduler_state == SCHED_CHAN_WAITING_TO_WRITE ||
chan->scheduler_state == SCHED_CHAN_PENDING)) {
chan->scheduler_state = SCHED_CHAN_WAITING_TO_WRITE;
log_debug(LD_SCHED,
"Channel " U64_FORMAT " at %p entered waiting_to_write",
U64_PRINTF_ARG(chan->global_identifier), chan);
@ -346,8 +319,6 @@ scheduler_init(void)
run_sched_ev = tor_event_new(tor_libevent_get_base(), -1,
0, scheduler_evt_callback, NULL);
channels_waiting_for_cells = smartlist_new();
channels_waiting_to_write = smartlist_new();
channels_pending = smartlist_new();
queue_heuristic = 0;
queue_heuristic_timestamp = approx_time();
@ -379,14 +350,13 @@ void
scheduler_release_channel(channel_t *chan)
{
tor_assert(chan);
tor_assert(channels_waiting_for_cells);
tor_assert(channels_waiting_to_write);
tor_assert(channels_pending);
smartlist_remove(channels_waiting_for_cells, chan);
smartlist_remove(channels_waiting_to_write, chan);
smartlist_remove(channels_pending, chan);
if (chan->scheduler_state == SCHED_CHAN_PENDING) {
smartlist_remove(channels_pending, chan);
}
chan->scheduler_state = SCHED_CHAN_IDLE;
}
/** Run the scheduling algorithm if necessary */
@ -432,6 +402,13 @@ scheduler_run(void)
flushed += flushed_this_time;
}
if (flushed < n_cells) {
/* We ran out of cells to flush */
chan->scheduler_state = SCHED_CHAN_WAITING_FOR_CELLS;
} else {
/* TODO get this right */
}
log_debug(LD_SCHED,
"Scheduler flushed %d cells onto pending channel "
U64_FORMAT " at %p",
@ -442,10 +419,13 @@ scheduler_run(void)
"Scheduler saw pending channel " U64_FORMAT " at %p with "
"no cells writeable",
U64_PRINTF_ARG(chan->global_identifier), chan);
/* Put it back to WAITING_TO_WRITE */
chan->scheduler_state = SCHED_CHAN_WAITING_TO_WRITE;
}
} else {
/* Not getting it this round; put it back on the list */
smartlist_add(channels_pending, chan);
/* It states in SCHED_CHAN_PENDING */
}
} SMARTLIST_FOREACH_END(chan);
@ -486,18 +466,15 @@ scheduler_channel_wants_writes(channel_t *chan)
int became_pending = 0;
tor_assert(chan);
tor_assert(channels_waiting_for_cells);
tor_assert(channels_waiting_to_write);
tor_assert(channels_pending);
/* If it's already in waiting_to_write, we can put it in pending */
if (smartlist_contains(channels_waiting_to_write, chan)) {
if (chan->scheduler_state == SCHED_CHAN_WAITING_TO_WRITE) {
/*
* It's in channels_waiting_to_write, so it shouldn't be in any of
* the other lists. It can write now, so it goes to channels_pending.
* It can write now, so it goes to channels_pending.
*/
smartlist_remove(channels_waiting_to_write, chan);
smartlist_add(channels_pending, chan);
chan->scheduler_state = SCHED_CHAN_PENDING;
log_debug(LD_SCHED,
"Channel " U64_FORMAT " at %p went from waiting_to_write "
"to pending",
@ -505,13 +482,12 @@ scheduler_channel_wants_writes(channel_t *chan)
became_pending = 1;
} else {
/*
* It's not in waiting_to_write, so it can't become pending; it's
* either not in any of the lists (we add it to waiting_for_cells)
* or it's already in waiting_for_cells or pending (we do nothing)
* It's not in SCHED_CHAN_WAITING_TO_WRITE, so it can't become pending;
* it's either idle and goes to WAITING_FOR_CELLS, or it's a no-op.
*/
if (!(smartlist_contains(channels_waiting_for_cells, chan) ||
smartlist_contains(channels_pending, chan))) {
smartlist_add(channels_waiting_for_cells, chan);
if (!(chan->scheduler_state == SCHED_CHAN_WAITING_FOR_CELLS ||
chan->scheduler_state == SCHED_CHAN_PENDING)) {
chan->scheduler_state = SCHED_CHAN_WAITING_FOR_CELLS;
log_debug(LD_SCHED,
"Channel " U64_FORMAT " at %p entered waiting_for_cells",
U64_PRINTF_ARG(chan->global_identifier), chan);