Cody Schuffelen | 134ff03 | 2019-11-22 00:25:32 -0800 | [diff] [blame^] | 1 | #include "common/vsoc/lib/region_view.h" |
| 2 | |
| 3 | #include <sys/mman.h> |
| 4 | |
| 5 | #include "common/libs/glog/logging.h" |
| 6 | |
| 7 | namespace { |
| 8 | const uint32_t UADDR_OFFSET_MASK = 0xFFFFFFFC; |
| 9 | const uint32_t UADDR_OFFSET_ROUND_TRIP_FLAG = 1; |
| 10 | } // namespace |
| 11 | |
| 12 | using vsoc::layout::Sides; |
| 13 | |
| 14 | vsoc::RegionWorker::RegionWorker(RegionView* region, |
| 15 | std::shared_ptr<RegionControl> control) |
| 16 | : control_(control), |
| 17 | region_(region), |
| 18 | stopping_(false) {} |
| 19 | |
| 20 | void vsoc::RegionWorker::start() { |
| 21 | CHECK(!thread_.joinable()); |
| 22 | thread_ = std::thread(&vsoc::RegionWorker::Work, this); |
| 23 | } |
| 24 | |
| 25 | void vsoc::RegionWorker::Work() { |
| 26 | while (!stopping_) { |
| 27 | region_->WaitForInterrupt(); |
| 28 | if (stopping_) { |
| 29 | return; |
| 30 | } |
| 31 | region_->ProcessSignalsFromPeer([this](uint32_t offset) { |
| 32 | control_->SignalSelf(offset); |
| 33 | }); |
| 34 | } |
| 35 | } |
| 36 | |
| 37 | vsoc::RegionWorker::~RegionWorker() { |
| 38 | stopping_ = true; |
| 39 | |
| 40 | if (thread_.joinable()) { |
| 41 | region_->InterruptSelf(); |
| 42 | thread_.join(); |
| 43 | } |
| 44 | } |
| 45 | |
| 46 | vsoc::RegionView::~RegionView() { |
| 47 | // region_base_ is borrowed here. It's owned by control_, which is |
| 48 | // responsible for unmapping the memory |
| 49 | region_base_ = nullptr; |
| 50 | } |
| 51 | |
| 52 | #if defined(CUTTLEFISH_HOST) |
| 53 | bool vsoc::RegionView::Open(const char* name, const char* domain) { |
| 54 | control_ = vsoc::RegionControl::Open(name, domain); |
| 55 | if (!control_) { |
| 56 | return false; |
| 57 | } |
| 58 | region_base_ = control_->Map(); |
| 59 | return region_base_ != nullptr; |
| 60 | } |
| 61 | #else |
| 62 | bool vsoc::RegionView::Open(const char* name) { |
| 63 | control_ = vsoc::RegionControl::Open(name); |
| 64 | if (!control_) { |
| 65 | return false; |
| 66 | } |
| 67 | region_base_ = control_->Map(); |
| 68 | return region_base_ != nullptr; |
| 69 | } |
| 70 | #endif |
| 71 | |
| 72 | // Interrupt our peer, causing it to scan the outgoing_signal_table |
| 73 | bool vsoc::RegionView::MaybeInterruptPeer() { |
| 74 | if (region_offset_to_pointer<std::atomic<uint32_t>>( |
| 75 | outgoing_signal_table().interrupt_signalled_offset) |
| 76 | ->exchange(1)) { |
| 77 | return false; |
| 78 | } |
| 79 | return control_->InterruptPeer(); |
| 80 | } |
| 81 | |
| 82 | // Wait for an interrupt from our peer |
| 83 | void vsoc::RegionView::WaitForInterrupt() { |
| 84 | while (1) { |
| 85 | if (region_offset_to_pointer<std::atomic<uint32_t>>( |
| 86 | incoming_signal_table().interrupt_signalled_offset) |
| 87 | ->exchange(0)) { |
| 88 | return; |
| 89 | } |
| 90 | control_->WaitForInterrupt(); |
| 91 | } |
| 92 | } |
| 93 | |
| 94 | void vsoc::RegionView::ProcessSignalsFromPeer( |
| 95 | std::function<void(uint32_t)> signal_handler) { |
| 96 | const vsoc_signal_table_layout& table = incoming_signal_table(); |
| 97 | const size_t num_offsets = (1 << table.num_nodes_lg2); |
| 98 | std::atomic<uint32_t>* offsets = |
| 99 | region_offset_to_pointer<std::atomic<uint32_t>>( |
| 100 | table.futex_uaddr_table_offset); |
| 101 | for (size_t i = 0; i < num_offsets; ++i) { |
| 102 | uint32_t raw_offset = offsets[i].exchange(0); |
| 103 | if (raw_offset) { |
| 104 | bool round_trip = raw_offset & UADDR_OFFSET_ROUND_TRIP_FLAG; |
| 105 | uint32_t offset = raw_offset & UADDR_OFFSET_MASK; |
| 106 | signal_handler(offset); |
| 107 | if (round_trip) { |
| 108 | SendSignalToPeer( |
| 109 | region_offset_to_pointer<std::atomic<uint32_t>>(offset), false); |
| 110 | } |
| 111 | } |
| 112 | } |
| 113 | } |
| 114 | |
| 115 | void vsoc::RegionView::SendSignal(Sides sides_to_signal, |
| 116 | std::atomic<uint32_t>* uaddr) { |
| 117 | if (sides_to_signal & Sides::Peer) { |
| 118 | // If we should also be signalling our side set the round trip flag on |
| 119 | // the futex signal. |
| 120 | bool round_trip = sides_to_signal & Sides::OurSide; |
| 121 | SendSignalToPeer(uaddr, round_trip); |
| 122 | // Return without signaling our waiters to give the other side a chance |
| 123 | // to run. |
| 124 | return; |
| 125 | } |
| 126 | if (sides_to_signal & Sides::OurSide) { |
| 127 | control_->SignalSelf(pointer_to_region_offset(uaddr)); |
| 128 | } |
| 129 | } |
| 130 | |
| 131 | void vsoc::RegionView::SendSignalToPeer(std::atomic<uint32_t>* uaddr, |
| 132 | bool round_trip) { |
| 133 | const vsoc_signal_table_layout& table = outgoing_signal_table(); |
| 134 | std::atomic<uint32_t>* offsets = |
| 135 | region_offset_to_pointer<std::atomic<uint32_t>>( |
| 136 | table.futex_uaddr_table_offset); |
| 137 | // maximum index in the node that can hold an offset; |
| 138 | const size_t max_index = (1 << table.num_nodes_lg2) - 1; |
| 139 | uint32_t offset = pointer_to_region_offset(uaddr); |
| 140 | if (offset & ~UADDR_OFFSET_MASK) { |
| 141 | LOG(FATAL) << "uaddr offset is not naturally aligned " << uaddr; |
| 142 | } |
| 143 | // Guess at where this offset should go in the table. |
| 144 | // Do this before we set the round-trip flag. |
| 145 | size_t hash = (offset >> 2) & max_index; |
| 146 | if (round_trip) { |
| 147 | offset |= UADDR_OFFSET_ROUND_TRIP_FLAG; |
| 148 | } |
| 149 | while (1) { |
| 150 | uint32_t expected = 0; |
| 151 | if (offsets[hash].compare_exchange_strong(expected, offset)) { |
| 152 | // We stored the offset. Send the interrupt. |
| 153 | this->MaybeInterruptPeer(); |
| 154 | break; |
| 155 | } |
| 156 | // We didn't store, but the value was already in the table with our flag. |
| 157 | // Return without interrupting. |
| 158 | if (expected == offset) { |
| 159 | return; |
| 160 | } |
| 161 | // Hash collision. Try again in a different node |
| 162 | if ((expected & UADDR_OFFSET_MASK) != (offset & UADDR_OFFSET_MASK)) { |
| 163 | hash = (hash + 1) & max_index; |
| 164 | continue; |
| 165 | } |
| 166 | // Our offset was in the bucket, but the flags didn't match. |
| 167 | // We're done if the value in the node had the round trip flag set. |
| 168 | if (expected & UADDR_OFFSET_ROUND_TRIP_FLAG) { |
| 169 | return; |
| 170 | } |
| 171 | // We wanted the round trip flag, but the value in the bucket didn't set it. |
| 172 | // Do a second swap to try to set it. |
| 173 | if (offsets[hash].compare_exchange_strong(expected, offset)) { |
| 174 | // It worked. We're done. |
| 175 | return; |
| 176 | } |
| 177 | if (expected == offset) { |
| 178 | // expected was the offset without the flag. After the swap it has the |
| 179 | // the flag. This means that some other thread set the flag, so |
| 180 | // we're done. |
| 181 | return; |
| 182 | } |
| 183 | // Something about the offset changed. We need to go around again, because: |
| 184 | // our peer processed the old entry |
| 185 | // another thread may have stolen the node while we were distracted |
| 186 | } |
| 187 | } |
| 188 | |
| 189 | std::unique_ptr<vsoc::RegionWorker> vsoc::RegionView::StartWorker() { |
| 190 | std::unique_ptr<vsoc::RegionWorker> worker( |
| 191 | new vsoc::RegionWorker(this /* region */, control_)); |
| 192 | |
| 193 | worker->start(); |
| 194 | return worker; |
| 195 | } |
| 196 | |
| 197 | int vsoc::RegionView::WaitForSignal(std::atomic<uint32_t>* uaddr, |
| 198 | uint32_t expected_value) { |
| 199 | return control_->WaitForSignal(pointer_to_region_offset(uaddr), |
| 200 | expected_value); |
| 201 | } |