Automatic resolution throttling for screen capture pipeline.

media/capture/thread_safe_capture_oracle.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "media/capture/thread_safe_capture_oracle.h"
 
 #include "base/basictypes.h"
 #include "base/bind.h"
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/synchronization/lock.h"
 #include "base/time/time.h"
 #include "base/trace_event/trace_event.h"
 #include "media/base/video_capture_types.h"
 #include "media/base/video_frame.h"
 #include "media/base/video_frame_metadata.h"
 #include "media/base/video_util.h"
 #include "ui/gfx/geometry/rect.h"
 
 namespace media {
 
+namespace {
+
+// The target maximum amount of the buffer pool to utilize.  Actual buffer pool
+// utilization is attenuated by this amount before being reported to the
+// VideoCaptureOracle.  This value takes into account the maximum number of
+// buffer pool buffers and a desired safety margin.
+const int kTargetMaxPoolUtilizationPercent = 60;
+
+}  // namespace
+
 ThreadSafeCaptureOracle::ThreadSafeCaptureOracle(
     scoped_ptr<VideoCaptureDevice::Client> client,
     const VideoCaptureParams& params)
     : client_(client.Pass()),
       oracle_(base::TimeDelta::FromMicroseconds(
           static_cast<int64>(1000000.0 / params.requested_format.frame_rate +
-                             0.5 /* to round to nearest int */))),
-      params_(params),
-      resolution_chooser_(params.requested_format.frame_size,
-                          params.resolution_change_policy) {}
+                             0.5 /* to round to nearest int */)),
+          params.requested_format.frame_size,
+          params.resolution_change_policy),
+      params_(params) {}
 
 ThreadSafeCaptureOracle::~ThreadSafeCaptureOracle() {}
 
 bool ThreadSafeCaptureOracle::ObserveEventAndDecideCapture(
     VideoCaptureOracle::Event event,
     const gfx::Rect& damage_rect,
     base::TimeTicks event_time,
     scoped_refptr<VideoFrame>* storage,
     CaptureFrameCallback* callback) {
   // Grab the current time before waiting to acquire the |lock_|.
   const base::TimeTicks capture_begin_time = base::TimeTicks::Now();
 
   base::AutoLock guard(lock_);
 
   if (!client_)
     return false;  // Capture is stopped.
 
-  const gfx::Size visible_size = resolution_chooser_.capture_size();
+  const bool should_capture =
+      oracle_.ObserveEventAndDecideCapture(event, damage_rect, event_time);
+  const gfx::Size visible_size = oracle_.capture_size();
   // Always round up the coded size to multiple of 16 pixels.
   // See http://crbug.com/402151.
   const gfx::Size coded_size((visible_size.width() + 15) & ~15,
                              (visible_size.height() + 15) & ~15);
 
   scoped_ptr<VideoCaptureDevice::Client::Buffer> output_buffer(
       client_->ReserveOutputBuffer(params_.requested_format.pixel_format,
                                    coded_size));
-  // TODO(miu): Use current buffer pool utilization to drive automatic video
-  // resolution changes.  http://crbug.com/156767.
-  VLOG(2) << "Current buffer pool utilization is "
-          << (client_->GetBufferPoolUtilization() * 100.0) << '%';
-
-  const bool should_capture =
-      oracle_.ObserveEventAndDecideCapture(event, damage_rect, event_time);
+  // Get the current buffer pool utilization and attenuate it: The utilization
+  // reported to the oracle is in terms of a maximum sustainable amount (not the
+  // absolute maximum).
+  const double attenuated_utilization = client_->GetBufferPoolUtilization() /

[hubbe, 2015/06/23 20:04:30]

Multiplication is potentially faster than division.

[miu, 2015/06/25 20:48:59]

Eliminated one of the divisions.  If C++11 constexpr was supported on all
toolchains, I could eliminate more...

Bikeshedding discussion: Technically, float division is usually implemented in
hardware as "inverse the denominator, then multiply" because inverting a float
is as simple as negating the exponent.

+      (kTargetMaxPoolUtilizationPercent / 100.0);
 
   const char* event_name =
       (event == VideoCaptureOracle::kTimerPoll ? "poll" :
        (event == VideoCaptureOracle::kCompositorUpdate ? "gpu" :
        "unknown"));
 
   // Consider the various reasons not to initiate a capture.
   if (should_capture && !output_buffer.get()) {
     TRACE_EVENT_INSTANT1("gpu.capture",
                          "PipelineLimited",
                          TRACE_EVENT_SCOPE_THREAD,
                          "trigger",
                          event_name);
+    oracle_.RecordWillNotCapture(attenuated_utilization);
     return false;
   } else if (!should_capture && output_buffer.get()) {
     if (event == VideoCaptureOracle::kCompositorUpdate) {
       // This is a normal and acceptable way to drop a frame. We've hit our
       // capture rate limit: for example, the content is animating at 60fps but
       // we're capturing at 30fps.
       TRACE_EVENT_INSTANT1("gpu.capture", "FpsRateLimited",
                            TRACE_EVENT_SCOPE_THREAD,
                            "trigger", event_name);
     }
     return false;
   } else if (!should_capture && !output_buffer.get()) {
     // We decided not to capture, but we wouldn't have been able to if we wanted
     // to because no output buffer was available.
     TRACE_EVENT_INSTANT1("gpu.capture", "NearlyPipelineLimited",
                          TRACE_EVENT_SCOPE_THREAD,
                          "trigger", event_name);
     return false;
   }
-  int frame_number = oracle_.RecordCapture();
+  const int frame_number = oracle_.RecordCapture(attenuated_utilization);
   TRACE_EVENT_ASYNC_BEGIN2("gpu.capture", "Capture", output_buffer.get(),
                            "frame_number", frame_number,
                            "trigger", event_name);
   // NATIVE_TEXTURE frames wrap a texture mailbox, which we don't have at the
   // moment.  We do not construct those frames.
   if (params_.requested_format.pixel_format != PIXEL_FORMAT_TEXTURE) {
     *storage = VideoFrame::WrapExternalData(
         VideoFrame::I420,
         coded_size,
         gfx::Rect(visible_size),
         visible_size,
         static_cast<uint8*>(output_buffer->data()),
         output_buffer->size(),
         base::TimeDelta());
     DCHECK(*storage);
   }
   *callback = base::Bind(&ThreadSafeCaptureOracle::DidCaptureFrame,
                          this,
                          frame_number,
                          base::Passed(&output_buffer),
                          capture_begin_time,
                          oracle_.estimated_frame_duration());
   return true;
 }
 
 gfx::Size ThreadSafeCaptureOracle::GetCaptureSize() const {
   base::AutoLock guard(lock_);
-  return resolution_chooser_.capture_size();
+  return oracle_.capture_size();
 }
 
 void ThreadSafeCaptureOracle::UpdateCaptureSize(const gfx::Size& source_size) {
   base::AutoLock guard(lock_);
-  resolution_chooser_.SetSourceSize(source_size);
-  VLOG(1) << "Source size changed to " << source_size.ToString()
-          << " --> Capture size is now "
-          << resolution_chooser_.capture_size().ToString();
+  VLOG(1) << "Source size changed to " << source_size.ToString();
+  oracle_.SetSourceSize(source_size);
 }
 
 void ThreadSafeCaptureOracle::Stop() {
   base::AutoLock guard(lock_);
   client_.reset();
 }
 
 void ThreadSafeCaptureOracle::ReportError(const std::string& reason) {
   base::AutoLock guard(lock_);
   if (client_)
@@ skipping 43 matching lines @@
     int frame_number,
     const media::VideoFrameMetadata* metadata) {
   // Note: This function may be called on any thread by the VideoFrame
   // destructor.  |metadata| is still valid for read-access at this point.
   double utilization = -1.0;
   if (metadata->GetDouble(media::VideoFrameMetadata::RESOURCE_UTILIZATION,
                           &utilization) &&
       utilization >= 0.0) {
     VLOG(2) << "Consumer resource utilization for frame " << frame_number
             << ": " << utilization;
+
+    base::AutoLock guard(lock_);
+    oracle_.RecordConsumerFeedback(frame_number, utilization);
   }
-
-  // TODO(miu): Use |utilization| to drive automatic video resolution changes.
-  // http://crbug.com/156767.
 }
 
 }  // namespace media