diff options
Diffstat (limited to 'src/or/scheduler.c')
| -rw-r--r-- | src/or/scheduler.c | 115 |
1 files changed, 73 insertions, 42 deletions
diff --git a/src/or/scheduler.c b/src/or/scheduler.c index 49ac1b939a..fac545fba7 100644 --- a/src/or/scheduler.c +++ b/src/or/scheduler.c @@ -1,11 +1,6 @@ -/* * Copyright (c) 2013-2016, The Tor Project, Inc. */ +/* * Copyright (c) 2013-2017, The Tor Project, Inc. */ /* See LICENSE for licensing information */ -/** - * \file scheduler.c - * \brief Relay scheduling system - **/ - #include "or.h" #define TOR_CHANNEL_INTERNAL_ /* For channel_flush_some_cells() */ @@ -32,66 +27,102 @@ static uint32_t sched_q_high_water = 32768; static uint32_t sched_max_flush_cells = 16; -/* - * Write scheduling works by keeping track of which channels can +/** + * \file scheduler.c + * \brief Channel scheduling system: decides which channels should send and + * receive when. + * + * This module implements a scheduler algorithm, to decide + * which channels should send/receive when. + * + * The earliest versions of Tor approximated a kind of round-robin system + * among active connections, but only approximated it. + * + * Now, 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 have scheduler_state == - * SCHED_CHAN_IDLE - * - Transitions from: - * - Open for writes/has cells by simultaneously draining all circuit + * <ol> + * <li> + * Not open for writes, no cells to send. + * <ul><li> Not much to do here, and the channel will have scheduler_state + * == SCHED_CHAN_IDLE + * <li> Transitions from: + * <ul> + * <li>Open for writes/has cells by simultaneously draining all circuit * queues and filling the output buffer. - * - Transitions to: - * - Not open for writes/has cells by arrival of cells on an attached + * </ul> + * <li> Transitions to: + * <ul> + * <li> Not open for writes/has cells by arrival of cells on an attached * circuit (this would be driven from append_cell_to_circuit_queue()) - * - Open for writes/no cells by a channel type specific path; + * <li> Open for writes/no cells by a channel type specific path; * driven from connection_or_flushed_some() for channel_tls_t. + * </ul> + * </ul> * - * 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. It will have scheduler_state == - * SCHED_CHAN_WAITING_FOR_CELLS - * - Transitions from: - * - Not open for writes/no cells by flushing some of the output + * <li> Open for writes, no cells to send + * <ul> + * <li>Not much here either; this will be the state an idle but open + * channel can be expected to settle in. It will have scheduler_state + * == SCHED_CHAN_WAITING_FOR_CELLS + * <li> Transitions from: + * <ul> + * <li>Not open for writes/no cells by flushing some of the output * buffer. - * - Open for writes/has cells by the scheduler moving cells from + * <li>Open for writes/has cells by the scheduler moving cells from * circuit queues to channel output queue, but not having enough * to fill the output queue. - * - Transitions to: - * - Open for writes/has cells by arrival of new cells on an attached + * </ul> + * <li> Transitions to: + * <ul> + * <li>Open for writes/has cells by arrival of new cells on an attached * circuit, in append_cell_to_circuit_queue() + * </ul> + * </ul> * - * 3.) Not open for writes, cells to send - * - This is the state of a busy circuit limited by output bandwidth; + * <li>Not open for writes, cells to send + * <ul> + * <li>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 + * <li> Transitions from: + * <ul> + * <li>Not open for writes/no cells by arrival of cells on an attached * circuit - * - Open for writes/has cells by filling an output buffer without + * <li> Open for writes/has cells by filling an output buffer without * draining all cells from attached circuits - * - Transitions to: - * - Opens for writes/has cells by draining some of the output buffer + * </ul> + * <li> Transitions to: + * <ul> + * <li>Opens for writes/has cells by draining some of the output buffer * via the connection_or_flushed_some() path (for channel_tls_t). + * </ul> + * </ul> * - * 4.) Open for writes, cells to send - * - This connection is ready to relay some cells and waiting for + * <li>Open for writes, cells to send + * <ul> + * <li>This connection is ready to relay some cells and waiting for * 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() + * <li>Transitions from: + * <ul> + * <li> Not open for writes/has cells by the connection_or_flushed_some() * path - * - Open for writes/no cells by the append_cell_to_circuit_queue() + * <li> Open for writes/no cells by the append_cell_to_circuit_queue() * path - * - Transitions to: - * - Not open for writes/no cells by draining all circuit queues and - * simultaneously filling the output buffer. - * - Not open for writes/has cells by writing enough cells to fill the + * </ul> + * <li> Transitions to: + * <ul> + * <li>Not open for writes/no cells by draining all circuit queues and + * simultaneously filling the output buffer. + * <li>Not open for writes/has cells by writing enough cells to fill the * output buffer - * - Open for writes/no cells by draining all attached circuit queues + * <li>Open for writes/no cells by draining all attached circuit queues * without also filling the output buffer + * </ul> + * </ul> + * </ol> * * Other event-driven parts of the code move channels between these scheduling * states by calling scheduler functions; the scheduler only runs on open-for- |