commit 4a8a1f76ea6cbde128f2cda49049866ea739931d
Merge: c663716b6 506264791
Author: Nick Mathewson <nickm(a)torproject.org>
Date: Thu Feb 21 10:08:14 2019 -0500
Merge branch 'maint-0.3.4' into maint-0.3.5
changes/ticket29168 | 5 +++++
src/core/or/scheduler_kist.c | 2 +-
2 files changed, 6 insertions(+), 1 deletion(-)
diff --cc src/core/or/scheduler_kist.c
index e17d67cfd,000000000..79ecb0bc7
mode 100644,000000..100644
--- a/src/core/or/scheduler_kist.c
+++ b/src/core/or/scheduler_kist.c
@@@ -1,844 -1,0 +1,844 @@@
+/* Copyright (c) 2017-2019, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+#define SCHEDULER_KIST_PRIVATE
+
+#include "core/or/or.h"
+#include "lib/container/buffers.h"
+#include "app/config/config.h"
+#include "core/mainloop/connection.h"
+#include "feature/nodelist/networkstatus.h"
+#define TOR_CHANNEL_INTERNAL_
+#include "core/or/channel.h"
+#include "core/or/channeltls.h"
+#define SCHEDULER_PRIVATE_
+#include "core/or/scheduler.h"
+#include "lib/math/fp.h"
+
+#include "core/or/or_connection_st.h"
+
+#ifdef HAVE_SYS_IOCTL_H
+#include <sys/ioctl.h>
+#endif
+
+#ifdef HAVE_KIST_SUPPORT
+/* Kernel interface needed for KIST. */
+#include <netinet/tcp.h>
+#include <linux/sockios.h>
+#endif /* HAVE_KIST_SUPPORT */
+
+/*****************************************************************************
+ * Data structures and supporting functions
+ *****************************************************************************/
+
+/* Socket_table hash table stuff. The socket_table keeps track of per-socket
+ * limit information imposed by kist and used by kist. */
+
+static uint32_t
+socket_table_ent_hash(const socket_table_ent_t *ent)
+{
+ return (uint32_t)ent->chan->global_identifier;
+}
+
+static unsigned
+socket_table_ent_eq(const socket_table_ent_t *a, const socket_table_ent_t *b)
+{
+ return a->chan == b->chan;
+}
+
+typedef HT_HEAD(socket_table_s, socket_table_ent_s) socket_table_t;
+
+static socket_table_t socket_table = HT_INITIALIZER();
+
+HT_PROTOTYPE(socket_table_s, socket_table_ent_s, node, socket_table_ent_hash,
+ socket_table_ent_eq)
+HT_GENERATE2(socket_table_s, socket_table_ent_s, node, socket_table_ent_hash,
+ socket_table_ent_eq, 0.6, tor_reallocarray, tor_free_)
+
+/* outbuf_table hash table stuff. The outbuf_table keeps track of which
+ * channels have data sitting in their outbuf so the kist scheduler can force
+ * a write from outbuf to kernel periodically during a run and at the end of a
+ * run. */
+
+typedef struct outbuf_table_ent_s {
+ HT_ENTRY(outbuf_table_ent_s) node;
+ channel_t *chan;
+} outbuf_table_ent_t;
+
+static uint32_t
+outbuf_table_ent_hash(const outbuf_table_ent_t *ent)
+{
+ return (uint32_t)ent->chan->global_identifier;
+}
+
+static unsigned
+outbuf_table_ent_eq(const outbuf_table_ent_t *a, const outbuf_table_ent_t *b)
+{
+ return a->chan->global_identifier == b->chan->global_identifier;
+}
+
+HT_PROTOTYPE(outbuf_table_s, outbuf_table_ent_s, node, outbuf_table_ent_hash,
+ outbuf_table_ent_eq)
+HT_GENERATE2(outbuf_table_s, outbuf_table_ent_s, node, outbuf_table_ent_hash,
+ outbuf_table_ent_eq, 0.6, tor_reallocarray, tor_free_)
+
+/*****************************************************************************
+ * Other internal data
+ *****************************************************************************/
+
+/* Store the last time the scheduler was run so we can decide when to next run
+ * the scheduler based on it. */
+static monotime_t scheduler_last_run;
+/* This is a factor for the extra_space calculation in kist per-socket limits.
+ * It is the number of extra congestion windows we want to write to the kernel.
+ */
+static double sock_buf_size_factor = 1.0;
+/* How often the scheduler runs. */
+STATIC int sched_run_interval = KIST_SCHED_RUN_INTERVAL_DEFAULT;
+
+#ifdef HAVE_KIST_SUPPORT
+/* Indicate if KIST lite mode is on or off. We can disable it at runtime.
+ * Important to have because of the KISTLite -> KIST possible transition. */
+static unsigned int kist_lite_mode = 0;
+/* Indicate if we don't have the kernel support. This can happen if the kernel
+ * changed and it doesn't recognized the values passed to the syscalls needed
+ * by KIST. In that case, fallback to the naive approach. */
+static unsigned int kist_no_kernel_support = 0;
+#else /* !(defined(HAVE_KIST_SUPPORT)) */
+static unsigned int kist_lite_mode = 1;
+#endif /* defined(HAVE_KIST_SUPPORT) */
+
+/*****************************************************************************
+ * Internally called function implementations
+ *****************************************************************************/
+
+/* Little helper function to get the length of a channel's output buffer */
+static inline size_t
+channel_outbuf_length(channel_t *chan)
+{
+ tor_assert(chan);
+ /* In theory, this can not happen because we can not scheduler a channel
+ * without a connection that has its outbuf initialized. Just in case, bug
+ * on this so we can understand a bit more why it happened. */
+ if (SCHED_BUG(BASE_CHAN_TO_TLS(chan)->conn == NULL, chan)) {
+ return 0;
+ }
+ return buf_datalen(TO_CONN(BASE_CHAN_TO_TLS(chan)->conn)->outbuf);
+}
+
+/* Little helper function for HT_FOREACH_FN. */
+static int
+each_channel_write_to_kernel(outbuf_table_ent_t *ent, void *data)
+{
+ (void) data; /* Make compiler happy. */
+ channel_write_to_kernel(ent->chan);
+ return 0; /* Returning non-zero removes the element from the table. */
+}
+
+/* Free the given outbuf table entry ent. */
+static int
+free_outbuf_info_by_ent(outbuf_table_ent_t *ent, void *data)
+{
+ (void) data; /* Make compiler happy. */
+ log_debug(LD_SCHED, "Freeing outbuf table entry from chan=%" PRIu64,
+ ent->chan->global_identifier);
+ tor_free(ent);
+ return 1; /* So HT_FOREACH_FN will remove the element */
+}
+
+/* Free the given socket table entry ent. */
+static int
+free_socket_info_by_ent(socket_table_ent_t *ent, void *data)
+{
+ (void) data; /* Make compiler happy. */
+ log_debug(LD_SCHED, "Freeing socket table entry from chan=%" PRIu64,
+ ent->chan->global_identifier);
+ tor_free(ent);
+ return 1; /* So HT_FOREACH_FN will remove the element */
+}
+
+/* Clean up socket_table. Probably because the KIST sched impl is going away */
+static void
+free_all_socket_info(void)
+{
+ HT_FOREACH_FN(socket_table_s, &socket_table, free_socket_info_by_ent, NULL);
+ HT_CLEAR(socket_table_s, &socket_table);
+}
+
+static socket_table_ent_t *
+socket_table_search(socket_table_t *table, const channel_t *chan)
+{
+ socket_table_ent_t search, *ent = NULL;
+ search.chan = chan;
+ ent = HT_FIND(socket_table_s, table, &search);
+ return ent;
+}
+
+/* Free a socket entry in table for the given chan. */
+static void
+free_socket_info_by_chan(socket_table_t *table, const channel_t *chan)
+{
+ socket_table_ent_t *ent = NULL;
+ ent = socket_table_search(table, chan);
+ if (!ent)
+ return;
+ log_debug(LD_SCHED, "scheduler free socket info for chan=%" PRIu64,
+ chan->global_identifier);
+ HT_REMOVE(socket_table_s, table, ent);
+ free_socket_info_by_ent(ent, NULL);
+}
+
+/* Perform system calls for the given socket in order to calculate kist's
+ * per-socket limit as documented in the function body. */
+MOCK_IMPL(void,
+update_socket_info_impl, (socket_table_ent_t *ent))
+{
+#ifdef HAVE_KIST_SUPPORT
+ int64_t tcp_space, extra_space;
+ tor_assert(ent);
+ tor_assert(ent->chan);
+ const tor_socket_t sock =
+ TO_CONN(BASE_CHAN_TO_TLS((channel_t *) ent->chan)->conn)->s;
+ struct tcp_info tcp;
+ socklen_t tcp_info_len = sizeof(tcp);
+
+ if (kist_no_kernel_support || kist_lite_mode) {
+ goto fallback;
+ }
+
+ /* Gather information */
+ if (getsockopt(sock, SOL_TCP, TCP_INFO, (void *)&(tcp), &tcp_info_len) < 0) {
+ if (errno == EINVAL) {
+ /* Oops, this option is not provided by the kernel, we'll have to
+ * disable KIST entirely. This can happen if tor was built on a machine
+ * with the support previously or if the kernel was updated and lost the
+ * support. */
+ log_notice(LD_SCHED, "Looks like our kernel doesn't have the support "
+ "for KIST anymore. We will fallback to the naive "
+ "approach. Remove KIST from the Schedulers list "
+ "to disable.");
+ kist_no_kernel_support = 1;
+ }
+ goto fallback;
+ }
+ if (ioctl(sock, SIOCOUTQNSD, &(ent->notsent)) < 0) {
+ if (errno == EINVAL) {
+ log_notice(LD_SCHED, "Looks like our kernel doesn't have the support "
+ "for KIST anymore. We will fallback to the naive "
+ "approach. Remove KIST from the Schedulers list "
+ "to disable.");
+ /* Same reason as the above. */
+ kist_no_kernel_support = 1;
+ }
+ goto fallback;
+ }
+ ent->cwnd = tcp.tcpi_snd_cwnd;
+ ent->unacked = tcp.tcpi_unacked;
+ ent->mss = tcp.tcpi_snd_mss;
+
+ /* In order to reduce outbound kernel queuing delays and thus improve Tor's
+ * ability to prioritize circuits, KIST wants to set a socket write limit
+ * that is near the amount that the socket would be able to immediately send
+ * into the Internet.
+ *
+ * We first calculate how much the socket could send immediately (assuming
+ * completely full packets) according to the congestion window and the number
+ * of unacked packets.
+ *
+ * Then we add a little extra space in a controlled way. We do this so any
+ * when the kernel gets ACKs back for data currently sitting in the "TCP
+ * space", it will already have some more data to send immediately. It will
+ * not have to wait for the scheduler to run again. The amount of extra space
+ * is a factor of the current congestion window. With the suggested
+ * sock_buf_size_factor value of 1.0, we allow at most 2*cwnd bytes to sit in
+ * the kernel: 1 cwnd on the wire waiting for ACKs and 1 cwnd ready and
+ * waiting to be sent when those ACKs finally come.
+ *
+ * In the below diagram, we see some bytes in the TCP-space (denoted by '*')
+ * that have be sent onto the wire and are waiting for ACKs. We have a little
+ * more room in "TCP space" that we can fill with data that will be
+ * immediately sent. We also see the "extra space" KIST calculates. The sum
+ * of the empty "TCP space" and the "extra space" is the kist-imposed write
+ * limit for this socket.
+ *
+ * <----------------kernel-outbound-socket-queue----------------|
+ * <*********---------------------------------------------------|
+ * |----TCP-space-----|----extra-space-----|
+ * |------------------|
+ * ^ ((cwnd - unacked) * mss) bytes
+ * |--------------------|
+ * ^ ((cwnd * mss) * factor) bytes
+ */
+
+ /* These values from the kernel are uint32_t, they will always fit into a
+ * int64_t tcp_space variable but if the congestion window cwnd is smaller
+ * than the unacked packets, the remaining TCP space is set to 0. */
+ if (ent->cwnd >= ent->unacked) {
+ tcp_space = (ent->cwnd - ent->unacked) * (int64_t)(ent->mss);
+ } else {
+ tcp_space = 0;
+ }
+
+ /* The clamp_double_to_int64 makes sure the first part fits into an int64_t.
+ * In fact, if sock_buf_size_factor is still forced to be >= 0 in config.c,
+ * then it will be positive for sure. Then we subtract a uint32_t. Getting a
+ * negative value is OK, see after how it is being handled. */
+ extra_space =
+ clamp_double_to_int64(
+ (ent->cwnd * (int64_t)ent->mss) * sock_buf_size_factor) -
- ent->notsent;
++ ent->notsent - (int64_t)channel_outbuf_length((channel_t *) ent->chan);
+ if ((tcp_space + extra_space) < 0) {
+ /* This means that the "notsent" queue is just too big so we shouldn't put
+ * more in the kernel for now. */
+ ent->limit = 0;
+ } else {
+ /* The positive sum of two int64_t will always fit into an uint64_t.
+ * And we know this will always be positive, since we checked above. */
+ ent->limit = (uint64_t)tcp_space + (uint64_t)extra_space;
+ }
+ return;
+
+#else /* !(defined(HAVE_KIST_SUPPORT)) */
+ goto fallback;
+#endif /* defined(HAVE_KIST_SUPPORT) */
+
+ fallback:
+ /* If all of a sudden we don't have kist support, we just zero out all the
+ * variables for this socket since we don't know what they should be. We
+ * also allow the socket to write as much as it can from the estimated
+ * number of cells the lower layer can accept, effectively returning it to
+ * Vanilla scheduler behavior. */
+ ent->cwnd = ent->unacked = ent->mss = ent->notsent = 0;
+ /* This function calls the specialized channel object (currently channeltls)
+ * and ask how many cells it can write on the outbuf which we then multiply
+ * by the size of the cells for this channel. The cast is because this
+ * function requires a non-const channel object, meh. */
+ ent->limit = channel_num_cells_writeable((channel_t *) ent->chan) *
+ (get_cell_network_size(ent->chan->wide_circ_ids) +
+ TLS_PER_CELL_OVERHEAD);
+}
+
+/* Given a socket that isn't in the table, add it.
+ * Given a socket that is in the table, re-init values that need init-ing
+ * every scheduling run
+ */
+static void
+init_socket_info(socket_table_t *table, const channel_t *chan)
+{
+ socket_table_ent_t *ent = NULL;
+ ent = socket_table_search(table, chan);
+ if (!ent) {
+ log_debug(LD_SCHED, "scheduler init socket info for chan=%" PRIu64,
+ chan->global_identifier);
+ ent = tor_malloc_zero(sizeof(*ent));
+ ent->chan = chan;
+ HT_INSERT(socket_table_s, table, ent);
+ }
+ ent->written = 0;
+}
+
+/* Add chan to the outbuf table if it isn't already in it. If it is, then don't
+ * do anything */
+static void
+outbuf_table_add(outbuf_table_t *table, channel_t *chan)
+{
+ outbuf_table_ent_t search, *ent;
+ search.chan = chan;
+ ent = HT_FIND(outbuf_table_s, table, &search);
+ if (!ent) {
+ log_debug(LD_SCHED, "scheduler init outbuf info for chan=%" PRIu64,
+ chan->global_identifier);
+ ent = tor_malloc_zero(sizeof(*ent));
+ ent->chan = chan;
+ HT_INSERT(outbuf_table_s, table, ent);
+ }
+}
+
+static void
+outbuf_table_remove(outbuf_table_t *table, channel_t *chan)
+{
+ outbuf_table_ent_t search, *ent;
+ search.chan = chan;
+ ent = HT_FIND(outbuf_table_s, table, &search);
+ if (ent) {
+ HT_REMOVE(outbuf_table_s, table, ent);
+ free_outbuf_info_by_ent(ent, NULL);
+ }
+}
+
+/* Set the scheduler running interval. */
+static void
+set_scheduler_run_interval(void)
+{
+ int old_sched_run_interval = sched_run_interval;
+ sched_run_interval = kist_scheduler_run_interval();
+ if (old_sched_run_interval != sched_run_interval) {
+ log_info(LD_SCHED, "Scheduler KIST changing its running interval "
+ "from %" PRId32 " to %" PRId32,
+ old_sched_run_interval, sched_run_interval);
+ }
+}
+
+/* Return true iff the channel hasn't hit its kist-imposed write limit yet */
+static int
+socket_can_write(socket_table_t *table, const channel_t *chan)
+{
+ socket_table_ent_t *ent = NULL;
+ ent = socket_table_search(table, chan);
+ if (SCHED_BUG(!ent, chan)) {
+ return 1; // Just return true, saying that kist wouldn't limit the socket
+ }
+
+ /* We previously calculated a write limit for this socket. In the below
+ * calculation, first determine how much room is left in bytes. Then divide
+ * that by the amount of space a cell takes. If there's room for at least 1
+ * cell, then KIST will allow the socket to write. */
+ int64_t kist_limit_space =
+ (int64_t) (ent->limit - ent->written) /
+ (CELL_MAX_NETWORK_SIZE + TLS_PER_CELL_OVERHEAD);
+ return kist_limit_space > 0;
+}
+
+/* Update the channel's socket kernel information. */
+static void
+update_socket_info(socket_table_t *table, const channel_t *chan)
+{
+ socket_table_ent_t *ent = NULL;
+ ent = socket_table_search(table, chan);
+ if (SCHED_BUG(!ent, chan)) {
+ return; // Whelp. Entry didn't exist for some reason so nothing to do.
+ }
+ update_socket_info_impl(ent);
+ log_debug(LD_SCHED, "chan=%" PRIu64 " updated socket info, limit: %" PRIu64
+ ", cwnd: %" PRIu32 ", unacked: %" PRIu32
+ ", notsent: %" PRIu32 ", mss: %" PRIu32,
+ ent->chan->global_identifier, ent->limit, ent->cwnd, ent->unacked,
+ ent->notsent, ent->mss);
+}
+
+/* Increment the channel's socket written value by the number of bytes. */
+static void
+update_socket_written(socket_table_t *table, channel_t *chan, size_t bytes)
+{
+ socket_table_ent_t *ent = NULL;
+ ent = socket_table_search(table, chan);
+ if (SCHED_BUG(!ent, chan)) {
+ return; // Whelp. Entry didn't exist so nothing to do.
+ }
+
+ log_debug(LD_SCHED, "chan=%" PRIu64 " wrote %lu bytes, old was %" PRIi64,
+ chan->global_identifier, (unsigned long) bytes, ent->written);
+
+ ent->written += bytes;
+}
+
+/*
+ * A naive KIST impl would write every single cell all the way to the kernel.
+ * That would take a lot of system calls. A less bad KIST impl would write a
+ * channel's outbuf to the kernel only when we are switching to a different
+ * channel. But if we have two channels with equal priority, we end up writing
+ * one cell for each and bouncing back and forth. This KIST impl avoids that
+ * by only writing a channel's outbuf to the kernel if it has 8 cells or more
+ * in it.
+ */
+MOCK_IMPL(int, channel_should_write_to_kernel,
+ (outbuf_table_t *table, channel_t *chan))
+{
+ outbuf_table_add(table, chan);
+ /* CELL_MAX_NETWORK_SIZE * 8 because we only want to write the outbuf to the
+ * kernel if there's 8 or more cells waiting */
+ return channel_outbuf_length(chan) > (CELL_MAX_NETWORK_SIZE * 8);
+}
+
+/* Little helper function to write a channel's outbuf all the way to the
+ * kernel */
+MOCK_IMPL(void, channel_write_to_kernel, (channel_t *chan))
+{
+ tor_assert(chan);
+ log_debug(LD_SCHED, "Writing %lu bytes to kernel for chan %" PRIu64,
+ (unsigned long)channel_outbuf_length(chan),
+ chan->global_identifier);
+ connection_handle_write(TO_CONN(BASE_CHAN_TO_TLS(chan)->conn), 0);
+}
+
+/* Return true iff the scheduler has work to perform. */
+static int
+have_work(void)
+{
+ smartlist_t *cp = get_channels_pending();
+ IF_BUG_ONCE(!cp) {
+ return 0; // channels_pending doesn't exist so... no work?
+ }
+ return smartlist_len(cp) > 0;
+}
+
+/* Function of the scheduler interface: free_all() */
+static void
+kist_free_all(void)
+{
+ free_all_socket_info();
+}
+
+/* Function of the scheduler interface: on_channel_free() */
+static void
+kist_on_channel_free_fn(const channel_t *chan)
+{
+ free_socket_info_by_chan(&socket_table, chan);
+}
+
+/* Function of the scheduler interface: on_new_consensus() */
+static void
+kist_scheduler_on_new_consensus(void)
+{
+ set_scheduler_run_interval();
+}
+
+/* Function of the scheduler interface: on_new_options() */
+static void
+kist_scheduler_on_new_options(void)
+{
+ sock_buf_size_factor = get_options()->KISTSockBufSizeFactor;
+
+ /* Calls kist_scheduler_run_interval which calls get_options(). */
+ set_scheduler_run_interval();
+}
+
+/* Function of the scheduler interface: init() */
+static void
+kist_scheduler_init(void)
+{
+ /* When initializing the scheduler, the last run could be 0 because it is
+ * declared static or a value in the past that was set when it was last
+ * used. In both cases, we want to initialize it to now so we don't risk
+ * using the value 0 which doesn't play well with our monotonic time
+ * interface.
+ *
+ * One side effect is that the first scheduler run will be at the next tick
+ * that is in now + 10 msec (KIST_SCHED_RUN_INTERVAL_DEFAULT) by default. */
+ monotime_get(&scheduler_last_run);
+
+ kist_scheduler_on_new_options();
+ IF_BUG_ONCE(sched_run_interval == 0) {
+ log_warn(LD_SCHED, "We are initing the KIST scheduler and noticed the "
+ "KISTSchedRunInterval is telling us to not use KIST. That's "
+ "weird! We'll continue using KIST, but at %" PRId32 "ms.",
+ KIST_SCHED_RUN_INTERVAL_DEFAULT);
+ sched_run_interval = KIST_SCHED_RUN_INTERVAL_DEFAULT;
+ }
+}
+
+/* Function of the scheduler interface: schedule() */
+static void
+kist_scheduler_schedule(void)
+{
+ struct monotime_t now;
+ struct timeval next_run;
+ int64_t diff;
+
+ if (!have_work()) {
+ return;
+ }
+ monotime_get(&now);
+
+ /* If time is really monotonic, we can never have now being smaller than the
+ * last scheduler run. The scheduler_last_run at first is set to 0.
+ * Unfortunately, not all platforms guarantee monotonic time so we log at
+ * info level but don't make it more noisy. */
+ diff = monotime_diff_msec(&scheduler_last_run, &now);
+ if (diff < 0) {
+ log_info(LD_SCHED, "Monotonic time between now and last run of scheduler "
+ "is negative: %" PRId64 ". Setting diff to 0.", diff);
+ diff = 0;
+ }
+ if (diff < sched_run_interval) {
+ next_run.tv_sec = 0;
+ /* Takes 1000 ms -> us. This will always be valid because diff can NOT be
+ * negative and can NOT be bigger than sched_run_interval so values can
+ * only go from 1000 usec (diff set to interval - 1) to 100000 usec (diff
+ * set to 0) for the maximum allowed run interval (100ms). */
+ next_run.tv_usec = (int) ((sched_run_interval - diff) * 1000);
+ /* Re-adding an event reschedules it. It does not duplicate it. */
+ scheduler_ev_add(&next_run);
+ } else {
+ scheduler_ev_active();
+ }
+}
+
+/* Function of the scheduler interface: run() */
+static void
+kist_scheduler_run(void)
+{
+ /* Define variables */
+ channel_t *chan = NULL; // current working channel
+ /* The last distinct chan served in a sched loop. */
+ channel_t *prev_chan = NULL;
+ int flush_result; // temporarily store results from flush calls
+ /* Channels to be re-adding to pending at the end */
+ smartlist_t *to_readd = NULL;
+ smartlist_t *cp = get_channels_pending();
+
+ outbuf_table_t outbuf_table = HT_INITIALIZER();
+
+ /* For each pending channel, collect new kernel information */
+ SMARTLIST_FOREACH_BEGIN(cp, const channel_t *, pchan) {
+ init_socket_info(&socket_table, pchan);
+ update_socket_info(&socket_table, pchan);
+ } SMARTLIST_FOREACH_END(pchan);
+
+ log_debug(LD_SCHED, "Running the scheduler. %d channels pending",
+ smartlist_len(cp));
+
+ /* The main scheduling loop. Loop until there are no more pending channels */
+ while (smartlist_len(cp) > 0) {
+ /* get best channel */
+ chan = smartlist_pqueue_pop(cp, scheduler_compare_channels,
+ offsetof(channel_t, sched_heap_idx));
+ if (SCHED_BUG(!chan, NULL)) {
+ /* Some-freaking-how a NULL got into the channels_pending. That should
+ * never happen, but it should be harmless to ignore it and keep looping.
+ */
+ continue;
+ }
+ outbuf_table_add(&outbuf_table, chan);
+
+ /* if we have switched to a new channel, consider writing the previous
+ * channel's outbuf to the kernel. */
+ if (!prev_chan) {
+ prev_chan = chan;
+ }
+ if (prev_chan != chan) {
+ if (channel_should_write_to_kernel(&outbuf_table, prev_chan)) {
+ channel_write_to_kernel(prev_chan);
+ outbuf_table_remove(&outbuf_table, prev_chan);
+ }
+ prev_chan = chan;
+ }
+
+ /* Only flush and write if the per-socket limit hasn't been hit */
+ if (socket_can_write(&socket_table, chan)) {
+ /* flush to channel queue/outbuf */
+ flush_result = (int)channel_flush_some_cells(chan, 1); // 1 for num cells
+ /* XXX: While flushing cells, it is possible that the connection write
+ * fails leading to the channel to be closed which triggers a release
+ * and free its entry in the socket table. And because of a engineering
+ * design issue, the error is not propagated back so we don't get an
+ * error at this point. So before we continue, make sure the channel is
+ * open and if not just ignore it. See #23751. */
+ if (!CHANNEL_IS_OPEN(chan)) {
+ /* Channel isn't open so we put it back in IDLE mode. It is either
+ * renegotiating its TLS session or about to be released. */
+ scheduler_set_channel_state(chan, SCHED_CHAN_IDLE);
+ continue;
+ }
+ /* flush_result has the # cells flushed */
+ if (flush_result > 0) {
+ update_socket_written(&socket_table, chan, flush_result *
+ (CELL_MAX_NETWORK_SIZE + TLS_PER_CELL_OVERHEAD));
+ } else {
+ /* XXX: This can happen because tor sometimes does flush in an
+ * opportunistic way cells from the circuit to the outbuf so the
+ * channel can end up here without having anything to flush nor needed
+ * to write to the kernel. Hopefully we'll fix that soon but for now
+ * we have to handle this case which happens kind of often. */
+ log_debug(LD_SCHED,
+ "We didn't flush anything on a chan that we think "
+ "can write and wants to write. The channel's state is '%s' "
+ "and in scheduler state '%s'. We're going to mark it as "
+ "waiting_for_cells (as that's most likely the issue) and "
+ "stop scheduling it this round.",
+ channel_state_to_string(chan->state),
+ get_scheduler_state_string(chan->scheduler_state));
+ scheduler_set_channel_state(chan, SCHED_CHAN_WAITING_FOR_CELLS);
+ continue;
+ }
+ }
+
+ /* Decide what to do with the channel now */
+
+ if (!channel_more_to_flush(chan) &&
+ !socket_can_write(&socket_table, chan)) {
+
+ /* Case 1: no more cells to send, and cannot write */
+
+ /*
+ * You might think we should put the channel in SCHED_CHAN_IDLE. And
+ * you're probably correct. While implementing KIST, we found that the
+ * scheduling system would sometimes lose track of channels when we did
+ * that. We suspect it has to do with the difference between "can't
+ * write because socket/outbuf is full" and KIST's "can't write because
+ * we've arbitrarily decided that that's enough for now." Sometimes
+ * channels run out of cells at the same time they hit their
+ * kist-imposed write limit and maybe the rest of Tor doesn't put the
+ * channel back in pending when it is supposed to.
+ *
+ * This should be investigated again. It is as simple as changing
+ * SCHED_CHAN_WAITING_FOR_CELLS to SCHED_CHAN_IDLE and seeing if Tor
+ * starts having serious throughput issues. Best done in shadow/chutney.
+ */
+ scheduler_set_channel_state(chan, SCHED_CHAN_WAITING_FOR_CELLS);
+ } else if (!channel_more_to_flush(chan)) {
+
+ /* Case 2: no more cells to send, but still open for writes */
+
+ scheduler_set_channel_state(chan, SCHED_CHAN_WAITING_FOR_CELLS);
+ } else if (!socket_can_write(&socket_table, chan)) {
+
+ /* Case 3: cells to send, but cannot write */
+
+ /*
+ * We want to write, but can't. If we left the channel in
+ * channels_pending, we would never exit the scheduling loop. We need to
+ * add it to a temporary list of channels to be added to channels_pending
+ * after the scheduling loop is over. They can hopefully be taken care of
+ * in the next scheduling round.
+ */
+ if (!to_readd) {
+ to_readd = smartlist_new();
+ }
+ smartlist_add(to_readd, chan);
+ } else {
+
+ /* Case 4: cells to send, and still open for writes */
+
+ scheduler_set_channel_state(chan, SCHED_CHAN_PENDING);
+ if (!SCHED_BUG(chan->sched_heap_idx != -1, chan)) {
+ smartlist_pqueue_add(cp, scheduler_compare_channels,
+ offsetof(channel_t, sched_heap_idx), chan);
+ }
+ }
+ } /* End of main scheduling loop */
+
+ /* Write the outbuf of any channels that still have data */
+ HT_FOREACH_FN(outbuf_table_s, &outbuf_table, each_channel_write_to_kernel,
+ NULL);
+ /* We are done with it. */
+ HT_FOREACH_FN(outbuf_table_s, &outbuf_table, free_outbuf_info_by_ent, NULL);
+ HT_CLEAR(outbuf_table_s, &outbuf_table);
+
+ log_debug(LD_SCHED, "len pending=%d, len to_readd=%d",
+ smartlist_len(cp),
+ (to_readd ? smartlist_len(to_readd) : -1));
+
+ /* Re-add any channels we need to */
+ if (to_readd) {
+ SMARTLIST_FOREACH_BEGIN(to_readd, channel_t *, readd_chan) {
+ scheduler_set_channel_state(readd_chan, SCHED_CHAN_PENDING);
+ if (!smartlist_contains(cp, readd_chan)) {
+ if (!SCHED_BUG(chan->sched_heap_idx != -1, chan)) {
+ /* XXXX Note that the check above is in theory redundant with
+ * the smartlist_contains check. But let's make sure we're
+ * not messing anything up, and leave them both for now. */
+ smartlist_pqueue_add(cp, scheduler_compare_channels,
+ offsetof(channel_t, sched_heap_idx), readd_chan);
+ }
+ }
+ } SMARTLIST_FOREACH_END(readd_chan);
+ smartlist_free(to_readd);
+ }
+
+ monotime_get(&scheduler_last_run);
+}
+
+/*****************************************************************************
+ * Externally called function implementations not called through scheduler_t
+ *****************************************************************************/
+
+/* Stores the kist scheduler function pointers. */
+static scheduler_t kist_scheduler = {
+ .type = SCHEDULER_KIST,
+ .free_all = kist_free_all,
+ .on_channel_free = kist_on_channel_free_fn,
+ .init = kist_scheduler_init,
+ .on_new_consensus = kist_scheduler_on_new_consensus,
+ .schedule = kist_scheduler_schedule,
+ .run = kist_scheduler_run,
+ .on_new_options = kist_scheduler_on_new_options,
+};
+
+/* Return the KIST scheduler object. If it didn't exists, return a newly
+ * allocated one but init() is not called. */
+scheduler_t *
+get_kist_scheduler(void)
+{
+ return &kist_scheduler;
+}
+
+/* Check the torrc (and maybe consensus) for the configured KIST scheduler run
+ * interval.
+ * - If torrc > 0, then return the positive torrc value (should use KIST, and
+ * should use the set value)
+ * - If torrc == 0, then look in the consensus for what the value should be.
+ * - If == 0, then return 0 (don't use KIST)
+ * - If > 0, then return the positive consensus value
+ * - If consensus doesn't say anything, return 10 milliseconds, default.
+ */
+int
+kist_scheduler_run_interval(void)
+{
+ int run_interval = get_options()->KISTSchedRunInterval;
+
+ if (run_interval != 0) {
+ log_debug(LD_SCHED, "Found KISTSchedRunInterval=%" PRId32 " in torrc. "
+ "Using that.", run_interval);
+ return run_interval;
+ }
+
+ log_debug(LD_SCHED, "KISTSchedRunInterval=0, turning to the consensus.");
+
+ /* Will either be the consensus value or the default. Note that 0 can be
+ * returned which means the consensus wants us to NOT use KIST. */
+ return networkstatus_get_param(NULL, "KISTSchedRunInterval",
+ KIST_SCHED_RUN_INTERVAL_DEFAULT,
+ KIST_SCHED_RUN_INTERVAL_MIN,
+ KIST_SCHED_RUN_INTERVAL_MAX);
+}
+
+/* Set KISTLite mode that is KIST without kernel support. */
+void
+scheduler_kist_set_lite_mode(void)
+{
+ kist_lite_mode = 1;
+ kist_scheduler.type = SCHEDULER_KIST_LITE;
+ log_info(LD_SCHED,
+ "Setting KIST scheduler without kernel support (KISTLite mode)");
+}
+
+/* Set KIST mode that is KIST with kernel support. */
+void
+scheduler_kist_set_full_mode(void)
+{
+ kist_lite_mode = 0;
+ kist_scheduler.type = SCHEDULER_KIST;
+ log_info(LD_SCHED,
+ "Setting KIST scheduler with kernel support (KIST mode)");
+}
+
+#ifdef HAVE_KIST_SUPPORT
+
+/* Return true iff the scheduler subsystem should use KIST. */
+int
+scheduler_can_use_kist(void)
+{
+ if (kist_no_kernel_support) {
+ /* We have no kernel support so we can't use KIST. */
+ return 0;
+ }
+
+ /* We do have the support, time to check if we can get the interval that the
+ * consensus can be disabling. */
+ int run_interval = kist_scheduler_run_interval();
+ log_debug(LD_SCHED, "Determined KIST sched_run_interval should be "
+ "%" PRId32 ". Can%s use KIST.",
+ run_interval, (run_interval > 0 ? "" : " not"));
+ return run_interval > 0;
+}
+
+#else /* !(defined(HAVE_KIST_SUPPORT)) */
+
+int
+scheduler_can_use_kist(void)
+{
+ return 0;
+}
+
+#endif /* defined(HAVE_KIST_SUPPORT) */
