Use Histogram algorithm to calculate DNS timeout.

Honor DnsConfig timeout if it exceeds 5s.

BUG=110197
TEST=net_unittests --gtest_filter=DnsSessionTest.HistogramTimeout*

Review URL: https://chromiumcodereview.appspot.com/20482002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@214235 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 30 insertions, 13 deletions

diff --git a/net/dns/dns_session.cc b/net/dns/dns_session.cc
index 67d5779..ea8b6a1 100644
--- a/net/dns/dns_session.cc
+++ b/net/dns/dns_session.cc
@@ -38,6 +38,8 @@ struct DnsSession::ServerStats {
   ServerStats(base::TimeDelta rtt_estimate_param, RttBuckets* buckets)
     : last_failure_count(0), rtt_estimate(rtt_estimate_param) {
     rtt_histogram.reset(new base::SampleVector(buckets));
+    // Seed histogram with 2 samples at |rtt_estimate| timeout.
+    rtt_histogram->Accumulate(rtt_estimate.InMilliseconds(), 2);
   }
 
   // Count of consecutive failures after last success.
@@ -209,18 +211,10 @@ void DnsSession::RecordServerStats() {
 
 
 base::TimeDelta DnsSession::NextTimeout(unsigned server_index, int attempt) {
-  DCHECK_LT(server_index, server_stats_.size());
-
-  base::TimeDelta timeout = config_.timeout;
-  // If this server has not responded successfully, then don't wait too long.
-  if (server_stats_[server_index]->last_success.is_null())
-    return timeout;
-
-  // The timeout doubles every full round (each nameserver once).
-  unsigned num_backoffs = attempt / config_.nameservers.size();
-
-  return std::min(timeout * (1 << num_backoffs),
-                  base::TimeDelta::FromMilliseconds(kMaxTimeoutMs));
+  // Respect config timeout if it exceeds |kMaxTimeoutMs|.
+  if (config_.timeout.InMilliseconds() >= kMaxTimeoutMs)
+    return config_.timeout;
+  return NextTimeoutFromHistogram(server_index, attempt);
 }
 
 // Allocate a socket, already connected to the server address.
diff --git a/net/dns/dns_session_unittest.cc b/net/dns/dns_session_unittest.cc
index d0a12f2..4662706 100644
--- a/net/dns/dns_session_unittest.cc
+++ b/net/dns/dns_session_unittest.cc
@@ -220,6 +220,29 @@ TEST_F(DnsSessionTest, AllocateFree) {
   EXPECT_TRUE(NoMoreEvents());
 }
 
-} // namespace
+// Expect default calculated timeout to be within 10ms of in DnsConfig.
+TEST_F(DnsSessionTest, HistogramTimeoutNormal) {
+  Initialize(2);
+  base::TimeDelta timeoutDelta = session_->NextTimeout(0, 0) - config_.timeout;
+  EXPECT_LT(timeoutDelta.InMilliseconds(), 10);
+}
+
+// Expect short calculated timeout to be within 10ms of in DnsConfig.
+TEST_F(DnsSessionTest, HistogramTimeoutShort) {
+  config_.timeout = base::TimeDelta::FromMilliseconds(15);
+  Initialize(2);
+  base::TimeDelta timeoutDelta = session_->NextTimeout(0, 0) - config_.timeout;
+  EXPECT_LT(timeoutDelta.InMilliseconds(), 10);
+}
+
+// Expect long calculated timeout to be equal to one in DnsConfig.
+TEST_F(DnsSessionTest, HistogramTimeoutLong) {
+  config_.timeout = base::TimeDelta::FromSeconds(15);
+  Initialize(2);
+  base::TimeDelta timeout = session_->NextTimeout(0, 0);
+  EXPECT_EQ(config_.timeout.InMilliseconds(), timeout.InMilliseconds());
+}
+
+}  // namespace
 
 } // namespace net