1 /*
2 *
3 * Copyright 2017 gRPC authors.
4 *
5 * Licensed under the Apache License, Version 2.0 (the "License");
6 * you may not use this file except in compliance with the License.
7 * You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 *
17 */
18
19 #include <grpc/support/port_platform.h>
20
21 #include "src/core/ext/transport/chttp2/transport/flow_control.h"
22
23 #include <inttypes.h>
24 #include <limits.h>
25 #include <math.h>
26 #include <string.h>
27
28 #include <string>
29
30 #include "absl/strings/str_format.h"
31
32 #include <grpc/support/alloc.h>
33 #include <grpc/support/log.h>
34
35 #include "src/core/ext/transport/chttp2/transport/internal.h"
36 #include "src/core/lib/gpr/string.h"
37
38 grpc_core::TraceFlag grpc_flowctl_trace(false, "flowctl");
39
40 namespace grpc_core {
41 namespace chttp2 {
42
43 TestOnlyTransportTargetWindowEstimatesMocker*
44 g_test_only_transport_target_window_estimates_mocker;
45
46 namespace {
47
48 static constexpr const int kTracePadding = 30;
49 static constexpr const uint32_t kMaxWindowUpdateSize = (1u << 31) - 1;
50
fmt_int64_diff_str(int64_t old_val,int64_t new_val)51 static char* fmt_int64_diff_str(int64_t old_val, int64_t new_val) {
52 std::string str;
53 if (old_val != new_val) {
54 str = absl::StrFormat("%" PRId64 " -> %" PRId64 "", old_val, new_val);
55 } else {
56 str = absl::StrFormat("%" PRId64 "", old_val);
57 }
58 return gpr_leftpad(str.c_str(), ' ', kTracePadding);
59 }
60
fmt_uint32_diff_str(uint32_t old_val,uint32_t new_val)61 static char* fmt_uint32_diff_str(uint32_t old_val, uint32_t new_val) {
62 std::string str;
63 if (old_val != new_val) {
64 str = absl::StrFormat("%" PRIu32 " -> %" PRIu32 "", old_val, new_val);
65 } else {
66 str = absl::StrFormat("%" PRIu32 "", old_val);
67 }
68 return gpr_leftpad(str.c_str(), ' ', kTracePadding);
69 }
70 } // namespace
71
Init(const char * reason,TransportFlowControl * tfc,StreamFlowControl * sfc)72 void FlowControlTrace::Init(const char* reason, TransportFlowControl* tfc,
73 StreamFlowControl* sfc) {
74 tfc_ = tfc;
75 sfc_ = sfc;
76 reason_ = reason;
77 remote_window_ = tfc->remote_window();
78 target_window_ = tfc->target_window();
79 announced_window_ = tfc->announced_window();
80 if (sfc != nullptr) {
81 remote_window_delta_ = sfc->remote_window_delta();
82 local_window_delta_ = sfc->local_window_delta();
83 announced_window_delta_ = sfc->announced_window_delta();
84 }
85 }
86
Finish()87 void FlowControlTrace::Finish() {
88 uint32_t acked_local_window =
89 tfc_->transport()->settings[GRPC_SENT_SETTINGS]
90 [GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE];
91 uint32_t remote_window =
92 tfc_->transport()->settings[GRPC_PEER_SETTINGS]
93 [GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE];
94 char* trw_str = fmt_int64_diff_str(remote_window_, tfc_->remote_window());
95 char* tlw_str = fmt_int64_diff_str(target_window_, tfc_->target_window());
96 char* taw_str =
97 fmt_int64_diff_str(announced_window_, tfc_->announced_window());
98 char* srw_str;
99 char* slw_str;
100 char* saw_str;
101 if (sfc_ != nullptr) {
102 srw_str = fmt_int64_diff_str(remote_window_delta_ + remote_window,
103 sfc_->remote_window_delta() + remote_window);
104 slw_str =
105 fmt_int64_diff_str(local_window_delta_ + acked_local_window,
106 sfc_->local_window_delta() + acked_local_window);
107 saw_str =
108 fmt_int64_diff_str(announced_window_delta_ + acked_local_window,
109 sfc_->announced_window_delta() + acked_local_window);
110 } else {
111 srw_str = gpr_leftpad("", ' ', kTracePadding);
112 slw_str = gpr_leftpad("", ' ', kTracePadding);
113 saw_str = gpr_leftpad("", ' ', kTracePadding);
114 }
115 gpr_log(GPR_DEBUG,
116 "%p[%u][%s] | %s | trw:%s, tlw:%s, taw:%s, srw:%s, slw:%s, saw:%s",
117 tfc_, sfc_ != nullptr ? sfc_->stream()->id : 0,
118 tfc_->transport()->is_client ? "cli" : "svr", reason_, trw_str,
119 tlw_str, taw_str, srw_str, slw_str, saw_str);
120 gpr_free(trw_str);
121 gpr_free(tlw_str);
122 gpr_free(taw_str);
123 gpr_free(srw_str);
124 gpr_free(slw_str);
125 gpr_free(saw_str);
126 }
127
UrgencyString(Urgency u)128 const char* FlowControlAction::UrgencyString(Urgency u) {
129 switch (u) {
130 case Urgency::NO_ACTION_NEEDED:
131 return "no action";
132 case Urgency::UPDATE_IMMEDIATELY:
133 return "update immediately";
134 case Urgency::QUEUE_UPDATE:
135 return "queue update";
136 default:
137 GPR_UNREACHABLE_CODE(return "unknown");
138 }
139 GPR_UNREACHABLE_CODE(return "unknown");
140 }
141
Trace(grpc_chttp2_transport * t) const142 void FlowControlAction::Trace(grpc_chttp2_transport* t) const {
143 char* iw_str = fmt_uint32_diff_str(
144 t->settings[GRPC_SENT_SETTINGS][GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE],
145 initial_window_size_);
146 char* mf_str = fmt_uint32_diff_str(
147 t->settings[GRPC_SENT_SETTINGS][GRPC_CHTTP2_SETTINGS_MAX_FRAME_SIZE],
148 max_frame_size_);
149 gpr_log(GPR_DEBUG, "t[%s], s[%s], iw:%s:%s mf:%s:%s",
150 UrgencyString(send_transport_update_),
151 UrgencyString(send_stream_update_),
152 UrgencyString(send_initial_window_update_), iw_str,
153 UrgencyString(send_max_frame_size_update_), mf_str);
154 gpr_free(iw_str);
155 gpr_free(mf_str);
156 }
157
TransportFlowControlDisabled(grpc_chttp2_transport * t)158 TransportFlowControlDisabled::TransportFlowControlDisabled(
159 grpc_chttp2_transport* t) {
160 remote_window_ = kMaxWindow;
161 target_initial_window_size_ = kMaxWindow;
162 announced_window_ = kMaxWindow;
163 t->settings[GRPC_PEER_SETTINGS][GRPC_CHTTP2_SETTINGS_MAX_FRAME_SIZE] =
164 kFrameSize;
165 t->settings[GRPC_SENT_SETTINGS][GRPC_CHTTP2_SETTINGS_MAX_FRAME_SIZE] =
166 kFrameSize;
167 t->settings[GRPC_ACKED_SETTINGS][GRPC_CHTTP2_SETTINGS_MAX_FRAME_SIZE] =
168 kFrameSize;
169 t->settings[GRPC_PEER_SETTINGS][GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE] =
170 kMaxWindow;
171 t->settings[GRPC_SENT_SETTINGS][GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE] =
172 kMaxWindow;
173 t->settings[GRPC_ACKED_SETTINGS][GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE] =
174 kMaxWindow;
175 }
176
TransportFlowControl(const grpc_chttp2_transport * t,bool enable_bdp_probe)177 TransportFlowControl::TransportFlowControl(const grpc_chttp2_transport* t,
178 bool enable_bdp_probe)
179 : t_(t),
180 enable_bdp_probe_(enable_bdp_probe),
181 bdp_estimator_(t->peer_string.c_str()),
182 pid_controller_(grpc_core::PidController::Args()
183 .set_gain_p(4)
184 .set_gain_i(8)
185 .set_gain_d(0)
186 .set_initial_control_value(TargetLogBdp())
187 .set_min_control_value(-1)
188 .set_max_control_value(25)
189 .set_integral_range(10)),
190 last_pid_update_(grpc_core::ExecCtx::Get()->Now()) {}
191
MaybeSendUpdate(bool writing_anyway)192 uint32_t TransportFlowControl::MaybeSendUpdate(bool writing_anyway) {
193 FlowControlTrace trace("t updt sent", this, nullptr);
194 const uint32_t target_announced_window =
195 static_cast<uint32_t>(target_window());
196 if ((writing_anyway || announced_window_ <= target_announced_window / 2) &&
197 announced_window_ != target_announced_window) {
198 const uint32_t announce = static_cast<uint32_t> GPR_CLAMP(
199 target_announced_window - announced_window_, 0, kMaxWindowUpdateSize);
200 announced_window_ += announce;
201 return announce;
202 }
203 return 0;
204 }
205
ValidateRecvData(int64_t incoming_frame_size)206 grpc_error* TransportFlowControl::ValidateRecvData(
207 int64_t incoming_frame_size) {
208 if (incoming_frame_size > announced_window_) {
209 return GRPC_ERROR_CREATE_FROM_COPIED_STRING(
210 absl::StrFormat("frame of size %" PRId64
211 " overflows local window of %" PRId64,
212 incoming_frame_size, announced_window_)
213 .c_str());
214 }
215 return GRPC_ERROR_NONE;
216 }
217
StreamFlowControl(TransportFlowControl * tfc,const grpc_chttp2_stream * s)218 StreamFlowControl::StreamFlowControl(TransportFlowControl* tfc,
219 const grpc_chttp2_stream* s)
220 : tfc_(tfc), s_(s) {}
221
RecvData(int64_t incoming_frame_size)222 grpc_error* StreamFlowControl::RecvData(int64_t incoming_frame_size) {
223 FlowControlTrace trace(" data recv", tfc_, this);
224
225 grpc_error* error = GRPC_ERROR_NONE;
226 error = tfc_->ValidateRecvData(incoming_frame_size);
227 if (error != GRPC_ERROR_NONE) return error;
228
229 uint32_t sent_init_window =
230 tfc_->transport()->settings[GRPC_SENT_SETTINGS]
231 [GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE];
232 uint32_t acked_init_window =
233 tfc_->transport()->settings[GRPC_ACKED_SETTINGS]
234 [GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE];
235
236 int64_t acked_stream_window = announced_window_delta_ + acked_init_window;
237 int64_t sent_stream_window = announced_window_delta_ + sent_init_window;
238 if (incoming_frame_size > acked_stream_window) {
239 if (incoming_frame_size <= sent_stream_window) {
240 gpr_log(GPR_ERROR,
241 "Incoming frame of size %" PRId64
242 " exceeds local window size of %" PRId64
243 ".\n"
244 "The (un-acked, future) window size would be %" PRId64
245 " which is not exceeded.\n"
246 "This would usually cause a disconnection, but allowing it due to"
247 "broken HTTP2 implementations in the wild.\n"
248 "See (for example) https://github.com/netty/netty/issues/6520.",
249 incoming_frame_size, acked_stream_window, sent_stream_window);
250 } else {
251 return GRPC_ERROR_CREATE_FROM_COPIED_STRING(
252 absl::StrFormat("frame of size %" PRId64
253 " overflows local window of %" PRId64,
254 incoming_frame_size, acked_stream_window)
255 .c_str());
256 }
257 }
258
259 UpdateAnnouncedWindowDelta(tfc_, -incoming_frame_size);
260 local_window_delta_ -= incoming_frame_size;
261 tfc_->CommitRecvData(incoming_frame_size);
262 return GRPC_ERROR_NONE;
263 }
264
MaybeSendUpdate()265 uint32_t StreamFlowControl::MaybeSendUpdate() {
266 FlowControlTrace trace("s updt sent", tfc_, this);
267 if (local_window_delta_ > announced_window_delta_) {
268 uint32_t announce = static_cast<uint32_t> GPR_CLAMP(
269 local_window_delta_ - announced_window_delta_, 0, kMaxWindowUpdateSize);
270 UpdateAnnouncedWindowDelta(tfc_, announce);
271 return announce;
272 }
273 return 0;
274 }
275
IncomingByteStreamUpdate(size_t max_size_hint,size_t have_already)276 void StreamFlowControl::IncomingByteStreamUpdate(size_t max_size_hint,
277 size_t have_already) {
278 FlowControlTrace trace("app st recv", tfc_, this);
279 uint32_t max_recv_bytes;
280 uint32_t sent_init_window =
281 tfc_->transport()->settings[GRPC_SENT_SETTINGS]
282 [GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE];
283
284 /* clamp max recv hint to an allowable size */
285 if (max_size_hint >= kMaxWindowUpdateSize - sent_init_window) {
286 max_recv_bytes = kMaxWindowUpdateSize - sent_init_window;
287 } else {
288 max_recv_bytes = static_cast<uint32_t>(max_size_hint);
289 }
290
291 /* account for bytes already received but unknown to higher layers */
292 if (max_recv_bytes >= have_already) {
293 max_recv_bytes -= static_cast<uint32_t>(have_already);
294 } else {
295 max_recv_bytes = 0;
296 }
297
298 /* add some small lookahead to keep pipelines flowing */
299 GPR_DEBUG_ASSERT(max_recv_bytes <= kMaxWindowUpdateSize - sent_init_window);
300 if (local_window_delta_ < max_recv_bytes) {
301 uint32_t add_max_recv_bytes =
302 static_cast<uint32_t>(max_recv_bytes - local_window_delta_);
303 local_window_delta_ += add_max_recv_bytes;
304 }
305 }
306
307 // Take in a target and modifies it based on the memory pressure of the system
AdjustForMemoryPressure(grpc_resource_quota * quota,double target)308 static double AdjustForMemoryPressure(grpc_resource_quota* quota,
309 double target) {
310 // do not increase window under heavy memory pressure.
311 double memory_pressure = grpc_resource_quota_get_memory_pressure(quota);
312 static const double kLowMemPressure = 0.1;
313 static const double kZeroTarget = 22;
314 static const double kHighMemPressure = 0.8;
315 static const double kMaxMemPressure = 0.9;
316 if (memory_pressure < kLowMemPressure && target < kZeroTarget) {
317 target = (target - kZeroTarget) * memory_pressure / kLowMemPressure +
318 kZeroTarget;
319 } else if (memory_pressure > kHighMemPressure) {
320 target *= 1 - GPR_MIN(1, (memory_pressure - kHighMemPressure) /
321 (kMaxMemPressure - kHighMemPressure));
322 }
323 return target;
324 }
325
TargetLogBdp()326 double TransportFlowControl::TargetLogBdp() {
327 return AdjustForMemoryPressure(
328 grpc_resource_user_quota(grpc_endpoint_get_resource_user(t_->ep)),
329 1 + log2(bdp_estimator_.EstimateBdp()));
330 }
331
SmoothLogBdp(double value)332 double TransportFlowControl::SmoothLogBdp(double value) {
333 grpc_millis now = grpc_core::ExecCtx::Get()->Now();
334 double bdp_error = value - pid_controller_.last_control_value();
335 const double dt = static_cast<double>(now - last_pid_update_) * 1e-3;
336 last_pid_update_ = now;
337 // Limit dt to 100ms
338 const double kMaxDt = 0.1;
339 return pid_controller_.Update(bdp_error, dt > kMaxDt ? kMaxDt : dt);
340 }
341
DeltaUrgency(int64_t value,grpc_chttp2_setting_id setting_id)342 FlowControlAction::Urgency TransportFlowControl::DeltaUrgency(
343 int64_t value, grpc_chttp2_setting_id setting_id) {
344 int64_t delta = value - static_cast<int64_t>(
345 t_->settings[GRPC_LOCAL_SETTINGS][setting_id]);
346 // TODO(ncteisen): tune this
347 if (delta != 0 && (delta <= -value / 5 || delta >= value / 5)) {
348 return FlowControlAction::Urgency::QUEUE_UPDATE;
349 } else {
350 return FlowControlAction::Urgency::NO_ACTION_NEEDED;
351 }
352 }
353
PeriodicUpdate()354 FlowControlAction TransportFlowControl::PeriodicUpdate() {
355 FlowControlAction action;
356 if (enable_bdp_probe_) {
357 // get bdp estimate and update initial_window accordingly.
358 // target might change based on how much memory pressure we are under
359 // TODO(ncteisen): experiment with setting target to be huge under low
360 // memory pressure.
361 double target = pow(2, SmoothLogBdp(TargetLogBdp()));
362 if (g_test_only_transport_target_window_estimates_mocker != nullptr) {
363 // Hook for simulating unusual flow control situations in tests.
364 target = g_test_only_transport_target_window_estimates_mocker
365 ->ComputeNextTargetInitialWindowSizeFromPeriodicUpdate(
366 target_initial_window_size_ /* current target */);
367 }
368 // Though initial window 'could' drop to 0, we keep the floor at 128
369 target_initial_window_size_ =
370 static_cast<int32_t> GPR_CLAMP(target, 128, INT32_MAX);
371
372 action.set_send_initial_window_update(
373 DeltaUrgency(target_initial_window_size_,
374 GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE),
375 static_cast<uint32_t>(target_initial_window_size_));
376
377 // get bandwidth estimate and update max_frame accordingly.
378 double bw_dbl = bdp_estimator_.EstimateBandwidth();
379 // we target the max of BDP or bandwidth in microseconds.
380 int32_t frame_size = static_cast<int32_t> GPR_CLAMP(
381 GPR_MAX((int32_t)GPR_CLAMP(bw_dbl, 0, INT_MAX) / 1000,
382 target_initial_window_size_),
383 16384, 16777215);
384 action.set_send_max_frame_size_update(
385 DeltaUrgency(static_cast<int64_t>(frame_size),
386 GRPC_CHTTP2_SETTINGS_MAX_FRAME_SIZE),
387 frame_size);
388 }
389 return UpdateAction(action);
390 }
391
UpdateAction(FlowControlAction action)392 FlowControlAction StreamFlowControl::UpdateAction(FlowControlAction action) {
393 // TODO(ncteisen): tune this
394 if (!s_->read_closed) {
395 uint32_t sent_init_window =
396 tfc_->transport()->settings[GRPC_SENT_SETTINGS]
397 [GRPC_CHTTP2_SETTINGS_INITIAL_WINDOW_SIZE];
398 if (local_window_delta_ > announced_window_delta_ &&
399 announced_window_delta_ + sent_init_window <= sent_init_window / 2) {
400 action.set_send_stream_update(
401 FlowControlAction::Urgency::UPDATE_IMMEDIATELY);
402 } else if (local_window_delta_ > announced_window_delta_) {
403 action.set_send_stream_update(FlowControlAction::Urgency::QUEUE_UPDATE);
404 }
405 }
406
407 return action;
408 }
409
410 } // namespace chttp2
411 } // namespace grpc_core
412