Merge branch 'rewrite-metrics' into merge-metrics

semenzato@chromium.org

derat@chromium.org

bsimonnet@chromium.org

Copyright (c) 2010 The Chromium OS Authors. All rights reserved.

Use of this source code is governed by a BSD-style license that can be

found in the LICENSE file.

The Chrome OS "metrics" package contains utilities for client-side user metric

collection.

When Chrome is installed, Chrome will take care of aggregating and uploading the

metrics to the UMA server.

When Chrome is not installed (embedded build) and the metrics_uploader USE flag

is set, metrics_daemon will aggregate and upload the metrics itself.

================================================================================

The Metrics Library: libmetrics

================================================================================

libmetrics is a small library that implements the basic C and C++ API for

metrics collection. All metrics collection is funneled through this library. The

easiest and recommended way for a client-side module to collect user metrics is

to link libmetrics and use its APIs to send metrics to Chrome for transport to

UMA. In order to use the library in a module, you need to do the following:

- Add a dependence (DEPEND and RDEPEND) on chromeos-base/metrics to the module's

  ebuild.

- Link the module with libmetrics (for example, by passing -lmetrics to the

  module's link command). Both libmetrics.so and libmetrics.a are built and

  installed under $SYSROOT/usr/lib/. Note that by default -lmetrics will link

  against libmetrics.so, which is preferred.

- To access the metrics library API in the module, include the

  <metrics/metrics_library.h> header file. The file is installed in

  $SYSROOT/usr/include/ when the metrics library is built and installed.

- The API is documented in metrics_library.h under src/platform/metrics/. Before

  using the API methods, a MetricsLibrary object needs to be constructed and

  initialized through its Init method.

  For more information on the C API see c_metrics_library.h.

- Samples are sent to Chrome only if the "/home/chronos/Consent To Send Stats"

  file exists or the metrics are declared enabled in the policy file (see the

  AreMetricsEnabled API method).

- On the target platform, shortly after the sample is sent, it should be visible

  in Chrome through "about:histograms".

================================================================================

Histogram Naming Convention

================================================================================

Use TrackerArea.MetricName. For example:

Platform.DailyUseTime

Network.TimeToDrop

================================================================================

Server Side

================================================================================

If the histogram data is visible in about:histograms, it will be sent by an

official Chrome build to UMA, assuming the user has opted into metrics

collection. To make the histogram visible on "chromedashboard", the histogram

description XML file needs to be updated (steps 2 and 3 after following the

"Details on how to add your own histograms" link under the Histograms tab).

Include the string "Chrome OS" in the histogram description so that it's easier

to distinguish Chrome OS specific metrics from general Chrome histograms.

The UMA server logs and keeps the collected field data even if the metric's name

is not added to the histogram XML. However, the dashboard histogram for that

metric will show field data as of the histogram XML update date; it will not

include data for older dates. If past data needs to be displayed, manual

server-side intervention is required. In other words, one should assume that

field data collection starts only after the histogram XML has been updated.

================================================================================

The Metrics Client: metrics_client

================================================================================

metrics_client is a simple shell command-line utility for sending histogram

samples and user actions. It's installed under /usr/bin on the target platform

and uses libmetrics to send the data to Chrome. The utility is useful for

generating metrics from shell scripts.

For usage information and command-line options, run "metrics_client" on the

target platform or look for "Usage:" in metrics_client.cc.

================================================================================

The Metrics Daemon: metrics_daemon

================================================================================

metrics_daemon is a daemon that runs in the background on the target platform

and is intended for passive or ongoing metrics collection, or metrics collection

requiring feedback from multiple modules. For example, it listens to D-Bus

signals related to the user session and screen saver states to determine if the

user is actively using the device or not and generates the corresponding

data. The metrics daemon uses libmetrics to send the data to Chrome.

The recommended way to generate metrics data from a module is to link and use

libmetrics directly. However, the module could instead send signals to or

communicate in some alternative way with the metrics daemon. Then the metrics

daemon needs to monitor for the relevant events and take appropriate action --

for example, aggregate data and send the histogram samples.

================================================================================

FAQ

================================================================================

Q. What should my histogram's |min| and |max| values be set at?

A. You should set the values to a range that covers the vast majority of samples

   that would appear in the field. Note that samples below the |min| will still

   be collected in the underflow bucket and samples above the |max| will end up

   in the overflow bucket. Also, the reported mean of the data will be correct

   regardless of the range.

Q. How many buckets should I use in my histogram?

A. You should allocate as many buckets as necessary to perform proper analysis

   on the collected data. Note, however, that the memory allocated in Chrome for

   each histogram is proportional to the number of buckets. Therefore, it is

   strongly recommended to keep this number low (e.g., 50 is normal, while 100

   is probably high).

Q. When should I use an enumeration (linear) histogram vs. a regular

   (exponential) histogram?

A. Enumeration histograms should really be used only for sampling enumerated

   events and, in some cases, percentages. Normally, you should use a regular

   histogram with exponential bucket layout that provides higher resolution at

   the low end of the range and lower resolution at the high end. Regular

   histograms are generally used for collecting performance data (e.g., timing,

   memory usage, power) as well as aggregated event counts.

# See http://dev.chromium.org/developers/contributing-code/watchlists for

# a description of this file's format.

# Please keep these keys in alphabetical order.

{

  'WATCHLIST_DEFINITIONS': {

    'all': {

      'filepath': '.',

    },

  },

  'WATCHLISTS': {

    'all': ['petkov@chromium.org',

                'semenzato@chromium.org',

                'sosa@chromium.org']

  },

}

// Copyright (c) 2010 The Chromium OS Authors. All rights reserved.

// Use of this source code is governed by a BSD-style license that can be

// found in the LICENSE file.

//

// C wrapper to libmetrics

//

#include "metrics/c_metrics_library.h"

#include <string>

#include "metrics/metrics_library.h"

extern "C" CMetricsLibrary CMetricsLibraryNew(void) {

  MetricsLibrary* lib = new MetricsLibrary;

  return reinterpret_cast<CMetricsLibrary>(lib);

}

extern "C" void CMetricsLibraryDelete(CMetricsLibrary handle) {

  MetricsLibrary* lib = reinterpret_cast<MetricsLibrary*>(handle);

  delete lib;

}

extern "C" void CMetricsLibraryInit(CMetricsLibrary handle) {

  MetricsLibrary* lib = reinterpret_cast<MetricsLibrary*>(handle);

  if (lib != NULL)

    lib->Init();

}

extern "C" int CMetricsLibrarySendToUMA(CMetricsLibrary handle,

                                        const char* name, int sample,

                                        int min, int max, int nbuckets) {

  MetricsLibrary* lib = reinterpret_cast<MetricsLibrary*>(handle);

  if (lib == NULL)

    return 0;

  return lib->SendToUMA(std::string(name), sample, min, max, nbuckets);

}

extern "C" int CMetricsLibrarySendEnumToUMA(CMetricsLibrary handle,

                                            const char* name, int sample,

                                            int max) {

  MetricsLibrary* lib = reinterpret_cast<MetricsLibrary*>(handle);

  if (lib == NULL)

    return 0;

  return lib->SendEnumToUMA(std::string(name), sample, max);

}

extern "C" int CMetricsLibrarySendSparseToUMA(CMetricsLibrary handle,

                                              const char* name, int sample) {

  MetricsLibrary* lib = reinterpret_cast<MetricsLibrary*>(handle);

  if (lib == NULL)

    return 0;

  return lib->SendSparseToUMA(std::string(name), sample);

}

extern "C" int CMetricsLibrarySendUserActionToUMA(CMetricsLibrary handle,

                                                  const char* action) {

  MetricsLibrary* lib = reinterpret_cast<MetricsLibrary*>(handle);

  if (lib == NULL)

    return 0;

  return lib->SendUserActionToUMA(std::string(action));

}

extern "C" int CMetricsLibrarySendCrashToUMA(CMetricsLibrary handle,

                                            const char* crash_kind) {

  MetricsLibrary* lib = reinterpret_cast<MetricsLibrary*>(handle);

  if (lib == NULL)

    return 0;

  return lib->SendCrashToUMA(crash_kind);

}

extern "C" int CMetricsLibraryAreMetricsEnabled(CMetricsLibrary handle) {

  MetricsLibrary* lib = reinterpret_cast<MetricsLibrary*>(handle);

  if (lib == NULL)

    return 0;

  return lib->AreMetricsEnabled();

}

// Copyright (c) 2010 The Chromium OS Authors. All rights reserved.

// Use of this source code is governed by a BSD-style license that can be

// found in the LICENSE file.

#ifndef METRICS_C_METRICS_LIBRARY_H_

#define METRICS_C_METRICS_LIBRARY_H_

#if defined(__cplusplus)

extern "C" {

#endif

typedef struct CMetricsLibraryOpaque* CMetricsLibrary;

// C wrapper for MetricsLibrary::MetricsLibrary.

CMetricsLibrary CMetricsLibraryNew(void);

// C wrapper for MetricsLibrary::~MetricsLibrary.

void CMetricsLibraryDelete(CMetricsLibrary handle);

// C wrapper for MetricsLibrary::Init.

void CMetricsLibraryInit(CMetricsLibrary handle);

// C wrapper for MetricsLibrary::SendToUMA.

int CMetricsLibrarySendToUMA(CMetricsLibrary handle,

                             const char* name, int sample,

                             int min, int max, int nbuckets);

// C wrapper for MetricsLibrary::SendEnumToUMA.

int CMetricsLibrarySendEnumToUMA(CMetricsLibrary handle,

                                 const char* name, int sample, int max);

// C wrapper for MetricsLibrary::SendSparseToUMA.

int CMetricsLibrarySendSparseToUMA(CMetricsLibrary handle,

                                   const char* name, int sample);

// C wrapper for MetricsLibrary::SendUserActionToUMA.

int CMetricsLibrarySendUserActionToUMA(CMetricsLibrary handle,

                                       const char* action);

// C wrapper for MetricsLibrary::SendCrashToUMA.

int CMetricsLibrarySendCrashToUMA(CMetricsLibrary handle,

                                  const char* crash_kind);

// C wrapper for MetricsLibrary::AreMetricsEnabled.

int CMetricsLibraryAreMetricsEnabled(CMetricsLibrary handle);

#if defined(__cplusplus)

}

#endif

#endif  // METRICS_C_METRICS_LIBRARY_H_