Allow a tad more race-induced histogram errors

base/metrics/histogram.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.
 
 // Histogram is an object that aggregates statistics, and can summarize them in
 // various forms, including ASCII graphical, HTML, and numerically (as a
 // vector of numbers corresponding to each of the aggregating buckets).
 // See header file for details and examples.
 
 #include "base/metrics/histogram.h"
@@ skipping 348 matching lines @@
     if (delta != delta64)
       delta = INT_MAX;  // Flag all giant errors as INT_MAX.
     // Since snapshots of histograms are taken asynchronously relative to
     // sampling (and snapped from different threads), it is pretty likely that
     // we'll catch a redundant count that doesn't match the sample count.  We
     // allow for a certain amount of slop before flagging this as an
     // inconsistency.  Even with an inconsistency, we'll snapshot it again (for
     // UMA in about a half hour, so we'll eventually get the data, if it was
     // not the result of a corruption.  If histograms show that 1 is "too tight"
     // then we may try to use 2 or 3 for this slop value.
-    const int kCommonRaceBasedCountMismatch = 1;
+    const int kCommonRaceBasedCountMismatch = 5;
     if (delta > 0) {
       UMA_HISTOGRAM_COUNTS("Histogram.InconsistentCountHigh", delta);
       if (delta > kCommonRaceBasedCountMismatch)
         inconsistencies |= COUNT_HIGH_ERROR;
     } else {
       DCHECK_GT(0, delta);
       UMA_HISTOGRAM_COUNTS("Histogram.InconsistentCountLow", -delta);
       if (-delta > kCommonRaceBasedCountMismatch)
         inconsistencies |= COUNT_LOW_ERROR;
     }
@@ skipping 944 matching lines @@
 
 // static
 StatisticsRecorder::HistogramMap* StatisticsRecorder::histograms_ = NULL;
 // static
 StatisticsRecorder::RangesMap* StatisticsRecorder::ranges_ = NULL;
 // static
 base::Lock* StatisticsRecorder::lock_ = NULL;
 // static
 bool StatisticsRecorder::dump_on_exit_ = false;
 }  // namespace base