QUIC - add new UMA histograms to help understand HPACK head of line blocking.

net/quic/quic_chromium_client_session.cc

 // Copyright (c) 2012 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 "net/quic/quic_chromium_client_session.h"
 
 #include <utility>
 
 #include "base/callback_helpers.h"
 #include "base/location.h"
@@ skipping 125 matching lines @@
     SpdyStreamId stream_id,
     SpdyStreamId promised_stream_id,
     NetLogCaptureMode capture_mode) {
   std::unique_ptr<base::DictionaryValue> dict(new base::DictionaryValue());
   dict->Set("headers", ElideSpdyHeaderBlockForNetLog(*headers, capture_mode));
   dict->SetInteger("id", stream_id);
   dict->SetInteger("promised_stream_id", promised_stream_id);
   return std::move(dict);
 }
 
+class HpackEncoderDebugVisitor : public QuicHeadersStream::HpackDebugVisitor {
+  void OnUseEntry(QuicTime::Delta elapsed) override {
+    UMA_HISTOGRAM_TIMES(
+        "Net.QuicHpackEncoderIndexedEntryAge",

[Alexei Svitkine (slow), 2016/05/24 18:00:30]

Nit: Maybe slightly more readable if you add another . in between:

Net.QuicHpackEncoder.IndexedEntryAge

If you make the change, also change the one below and histograms.xml.

[Buck, 2016/05/24 18:15:06]

Done.

+        base::TimeDelta::FromMicroseconds(elapsed.ToMicroseconds()));
+  }
+};
+
+class HpackDecoderDebugVisitor : public QuicHeadersStream::HpackDebugVisitor {
+  void OnUseEntry(QuicTime::Delta elapsed) override {
+    UMA_HISTOGRAM_TIMES(
+        "Net.QuicHpackDecoderIndexedEntryAge",
+        base::TimeDelta::FromMicroseconds(elapsed.ToMicroseconds()));
+  }
+};
+
 }  // namespace
 
 QuicChromiumClientSession::StreamRequest::StreamRequest() : stream_(nullptr) {}
 
 QuicChromiumClientSession::StreamRequest::~StreamRequest() {
   CancelRequest();
 }
 
 int QuicChromiumClientSession::StreamRequest::StartRequest(
     const base::WeakPtr<QuicChromiumClientSession>& session,
@@ skipping 205 matching lines @@
                               0, kMaxReordering, 50);
   if (stats.min_rtt_us > 100 * 1000) {
     UMA_HISTOGRAM_CUSTOM_COUNTS("Net.QuicSession.MaxReorderingTimeLongRtt",
                                 reordering, 0, kMaxReordering, 50);
   }
   UMA_HISTOGRAM_COUNTS(
       "Net.QuicSession.MaxReordering",
       static_cast<base::HistogramBase::Sample>(stats.max_sequence_reordering));
 }
 
+void QuicChromiumClientSession::Initialize() {
+  QuicClientSessionBase::Initialize();
+  headers_stream()->SetHpackEncoderDebugVisitor(
+      base::WrapUnique(new HpackEncoderDebugVisitor()));
+  headers_stream()->SetHpackDecoderDebugVisitor(
+      base::WrapUnique(new HpackDecoderDebugVisitor()));
+}
+
 void QuicChromiumClientSession::OnHeadersHeadOfLineBlocking(
     QuicTime::Delta delta) {
   UMA_HISTOGRAM_TIMES(
       "Net.QuicSession.HeadersHOLBlockedTime",
       base::TimeDelta::FromMicroseconds(delta.ToMicroseconds()));
 }
 
 void QuicChromiumClientSession::OnStreamFrame(const QuicStreamFrame& frame) {
   // Record total number of stream frames.
   UMA_HISTOGRAM_COUNTS("Net.QuicNumStreamFramesInPacket", 1);
@@ skipping 796 matching lines @@
 }
 
 void QuicChromiumClientSession::DeletePromised(
     QuicClientPromisedInfo* promised) {
   if (IsOpenStream(promised->id()))
     streams_pushed_and_claimed_count_++;
   QuicClientSessionBase::DeletePromised(promised);
 }
 
 }  // namespace net