transmission/libtransmission/bandwidth.cc

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// This file Copyright © 2008-2023 Mnemosyne LLC.
// It may be used under GPLv2 (SPDX: GPL-2.0-only), GPLv3 (SPDX: GPL-3.0-only),
// or any future license endorsed by Mnemosyne LLC.
// License text can be found in the licenses/ folder.
#include <algorithm>
#include <utility> // for std::swap()
#include <vector>
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#include <fmt/core.h>
#include "transmission.h"
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#include "bandwidth.h"
#include "crypto-utils.h"
#include "log.h"
#include "peer-io.h"
#include "tr-assert.h"
#include "utils.h" // tr_time_msec()
tr_bytes_per_second_t tr_bandwidth::getSpeedBytesPerSecond(RateControl& r, unsigned int interval_msec, uint64_t now)
{
if (now == 0)
{
now = tr_time_msec();
}
if (now != r.cache_time_)
{
uint64_t bytes = 0;
uint64_t const cutoff = now - interval_msec;
for (int i = r.newest_; r.date_[i] > cutoff;)
{
bytes += r.size_[i];
if (--i == -1)
{
i = HistorySize - 1; /* circular history */
}
if (i == r.newest_)
{
break; /* we've come all the way around */
}
}
r.cache_val_ = static_cast<tr_bytes_per_second_t>(bytes * 1000U / interval_msec);
r.cache_time_ = now;
}
return r.cache_val_;
}
void tr_bandwidth::notifyBandwidthConsumedBytes(uint64_t const now, RateControl* r, size_t size)
{
if (r->date_[r->newest_] + GranularityMSec >= now)
{
r->size_[r->newest_] += size;
}
else
{
if (++r->newest_ == HistorySize)
{
r->newest_ = 0;
}
r->date_[r->newest_] = now;
r->size_[r->newest_] = size;
}
/* invalidate cache_val*/
r->cache_time_ = 0;
}
// ---
tr_bandwidth::tr_bandwidth(tr_bandwidth* parent)
{
this->setParent(parent);
}
// ---
namespace
{
namespace deparent_helpers
{
void remove_child(std::vector<tr_bandwidth*>& v, tr_bandwidth* remove_me) noexcept
{
// the list isn't sorted -- so instead of erase()ing `it`,
// do the cheaper option of overwriting it with the final item
if (auto it = std::find(std::begin(v), std::end(v), remove_me); it != std::end(v))
{
*it = v.back();
v.resize(v.size() - 1);
}
}
} // namespace deparent_helpers
} // namespace
void tr_bandwidth::deparent() noexcept
{
using namespace deparent_helpers;
if (parent_ == nullptr)
{
return;
}
remove_child(parent_->children_, this);
parent_ = nullptr;
}
void tr_bandwidth::setParent(tr_bandwidth* new_parent)
{
TR_ASSERT(this != new_parent);
deparent();
if (new_parent != nullptr)
{
#ifdef TR_ENABLE_ASSERTS
TR_ASSERT(new_parent->parent_ != this);
auto& children = new_parent->children_;
TR_ASSERT(std::find(std::begin(children), std::end(children), this) == std::end(children)); // not already there
#endif
new_parent->children_.push_back(this);
this->parent_ = new_parent;
}
}
// ---
void tr_bandwidth::allocateBandwidth(
tr_priority_t parent_priority,
unsigned int period_msec,
std::vector<std::shared_ptr<tr_peerIo>>& peer_pool)
{
auto const priority = std::max(parent_priority, this->priority_);
// set the available bandwidth
for (auto const dir : { TR_UP, TR_DOWN })
{
if (auto& bandwidth = band_[dir]; bandwidth.is_limited_)
{
auto const next_pulse_speed = bandwidth.desired_speed_bps_;
bandwidth.bytes_left_ = next_pulse_speed * period_msec / 1000U;
}
}
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// add this bandwidth's peer, if any, to the peer pool
if (auto shared = this->peer_.lock(); shared)
{
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shared->set_priority(priority);
peer_pool.push_back(std::move(shared));
}
// traverse & repeat for the subtree
for (auto* child : this->children_)
{
child->allocateBandwidth(priority, period_msec, peer_pool);
}
}
void tr_bandwidth::phaseOne(std::vector<tr_peerIo*>& peers, tr_direction dir)
{
// First phase of IO. Tries to distribute bandwidth fairly to keep faster
// peers from starving the others.
tr_logAddTrace(fmt::format("{} peers to go round-robin for {}", peers.size(), dir == TR_UP ? "upload" : "download"));
// Shuffle the peers so they all have equal chance to be first in line.
thread_local auto urbg = tr_urbg<size_t>{};
std::shuffle(std::begin(peers), std::end(peers), urbg);
// Give each peer `Increment` bandwidth bytes to use. Repeat this
// process until we run out of bandwidth and/or peers that can use it.
for (size_t n_unfinished = std::size(peers); n_unfinished > 0U;)
{
for (size_t i = 0; i < n_unfinished;)
{
// Value of 3000 bytes chosen so that when using µTP we'll send a full-size
// frame right away and leave enough buffered data for the next frame to go
// out in a timely manner.
static auto constexpr Increment = size_t{ 3000 };
auto const bytes_used = peers[i]->flush(dir, Increment);
tr_logAddTrace(fmt::format("peer #{} of {} used {} bytes in this pass", i, n_unfinished, bytes_used));
if (bytes_used != Increment)
{
// peer is done writing for now; move it to the end of the list
std::swap(peers[i], peers[n_unfinished - 1]);
--n_unfinished;
}
else
{
++i;
}
}
}
}
void tr_bandwidth::allocate(unsigned int period_msec)
{
// keep these peers alive for the scope of this function
auto refs = std::vector<std::shared_ptr<tr_peerIo>>{};
auto peer_arrays = std::array<std::vector<tr_peerIo*>, 3>{};
auto& high = peer_arrays[0];
auto& normal = peer_arrays[1];
auto& low = peer_arrays[2];
// allocateBandwidth () is a helper function with two purposes:
// 1. allocate bandwidth to b and its subtree
// 2. accumulate an array of all the peerIos from b and its subtree.
this->allocateBandwidth(TR_PRI_LOW, period_msec, refs);
for (auto const& io : refs)
{
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io->flush_outgoing_protocol_msgs();
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switch (io->priority())
{
case TR_PRI_HIGH:
high.push_back(io.get());
[[fallthrough]];
case TR_PRI_NORMAL:
normal.push_back(io.get());
[[fallthrough]];
default:
low.push_back(io.get());
}
}
// First phase of IO. Tries to distribute bandwidth fairly to keep faster
// peers from starving the others. Loop through the peers, giving each a
// small chunk of bandwidth. Keep looping until we run out of bandwidth
// and/or peers that can use it
for (auto& peers : peer_arrays)
{
phaseOne(peers, TR_UP);
phaseOne(peers, TR_DOWN);
}
// Second phase of IO. To help us scale in high bandwidth situations,
// enable on-demand IO for peers with bandwidth left to burn.
// This on-demand IO is enabled until (1) the peer runs out of bandwidth,
// or (2) the next tr_bandwidth::allocate () call, when we start over again.
for (auto const& io : refs)
{
io->set_enabled(TR_UP, io->has_bandwidth_left(TR_UP));
io->set_enabled(TR_DOWN, io->has_bandwidth_left(TR_DOWN));
}
}
// ---
size_t tr_bandwidth::clamp(uint64_t now, tr_direction dir, size_t byte_count) const
{
TR_ASSERT(tr_isDirection(dir));
if (this->band_[dir].is_limited_)
{
byte_count = std::min(byte_count, this->band_[dir].bytes_left_);
/* if we're getting close to exceeding the speed limit,
* clamp down harder on the bytes available */
if (byte_count > 0)
{
if (now == 0)
{
now = tr_time_msec();
}
auto const current = this->getRawSpeedBytesPerSecond(now, TR_DOWN);
auto const desired = this->getDesiredSpeedBytesPerSecond(TR_DOWN);
auto const r = desired >= 1 ? static_cast<double>(current) / desired : 0.0;
if (r > 1.0)
{
byte_count = 0; // none left
}
else if (r > 0.9)
{
byte_count -= (byte_count / 5U); // cap at 80%
}
else if (r > 0.8)
{
byte_count -= (byte_count / 10U); // cap at 90%
}
}
}
if (this->parent_ != nullptr && this->band_[dir].honor_parent_limits_ && byte_count > 0)
{
byte_count = this->parent_->clamp(now, dir, byte_count);
}
return byte_count;
}
void tr_bandwidth::notifyBandwidthConsumed(tr_direction dir, size_t byte_count, bool is_piece_data, uint64_t now)
{
TR_ASSERT(tr_isDirection(dir));
Band* band = &this->band_[dir];
if (band->is_limited_ && is_piece_data)
{
band->bytes_left_ -= std::min(size_t{ band->bytes_left_ }, byte_count);
}
#ifdef DEBUG_DIRECTION
if (dir == DEBUG_DIRECTION && band_->isLimited)
{
fprintf(
stderr,
"%p consumed %5zu bytes of %5s data... was %6zu, now %6zu left\n",
this,
byte_count,
is_piece_data ? "piece" : "raw",
oldBytesLeft,
band_->bytesLeft);
}
#endif
notifyBandwidthConsumedBytes(now, &band->raw_, byte_count);
if (is_piece_data)
{
notifyBandwidthConsumedBytes(now, &band->piece_, byte_count);
}
if (this->parent_ != nullptr)
{
this->parent_->notifyBandwidthConsumed(dir, byte_count, is_piece_data, now);
}
}
// ---
tr_bandwidth_limits tr_bandwidth::getLimits() const
{
tr_bandwidth_limits limits;
limits.up_limit_KBps = tr_toSpeedKBps(this->getDesiredSpeedBytesPerSecond(TR_UP));
limits.down_limit_KBps = tr_toSpeedKBps(this->getDesiredSpeedBytesPerSecond(TR_DOWN));
limits.up_limited = this->isLimited(TR_UP);
limits.down_limited = this->isLimited(TR_DOWN);
return limits;
}
void tr_bandwidth::setLimits(tr_bandwidth_limits const* limits)
{
this->setDesiredSpeedBytesPerSecond(TR_UP, tr_toSpeedBytes(limits->up_limit_KBps));
this->setDesiredSpeedBytesPerSecond(TR_DOWN, tr_toSpeedBytes(limits->down_limit_KBps));
this->setLimited(TR_UP, limits->up_limited);
this->setLimited(TR_DOWN, limits->down_limited);
}