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Anudipa Maiti
2 parents b6baf2af ffa568d2
Showing 2 changed files with 49 additions and 14 deletions
figures/tables/tableALL.tex
results.tex
@@ -84,6 +84,7 @@
 \num{7} & \texttt{Android Calculator} & 9.189 \\
 \num{8} & \texttt{Twitter} & 8.645 \\
 \num{9} & \texttt{Chrome Browser} & 8.524 \\
+\num{10} & & \\
 \bottomrule
 \num{10} & \texttt{Yahoo Mail} & 3.287 \\
 \num{9} & \texttt{ESPN SportsCenter} & 3.184 \\
@@ -100,6 +101,8 @@
 \caption{\small \textbf{Apps sorted by foreground energy efficiency.}}
+\label{table-foreground}
+
 \end{subtable}%
 \begin{subtable}[t]{0.5\textwidth}
 {\small
@@ -117,6 +120,7 @@
 \num{7} & \texttt{Twitter} & 5610.394 \\
 \num{8} & \texttt{Android Clock} & 5085.873 \\
 \num{9} & \texttt{Yahoo Mail} & 5083.615 \\
+\num{10} & & \\
 \bottomrule
 \num{10} & \texttt{NFL Mobile} & 1275.985 \\
 \num{9} & \texttt{UB Parking} & 1071.529 \\
@@ -132,6 +136,8 @@
 }
 \caption{\small \textbf{Apps sorted by content energy efficiency.}}
+
+\label{table-content}
 \end{subtable}
 \caption{\small \textbf{Evaluating Components of a Value Measure.}
@@ -39,7 +39,7 @@ it through a survey completed by 47~experiment participants. Unfortunately,
 our results are inconclusive and open to several possible interpretations
 which we conclude by discussing.
-\subsection{Total Consumption}
+\subsection{Total Energy}
 \input{./figures/tables/tableALL.tex}
@@ -52,32 +52,61 @@ list of low consumers is dominated by apps with few installs. This table does
 serve, however, to identify the popular apps in use by \PhoneLab{}
 participants, and as a point of comparison for the remainder of our results.
-\subsection{Consumption Rate}
+\subsection{Power}
-Computing the rate at which apps consume energy by scaling their total energy
-usage against the total time they were running, either in the background or
+Computing each app's power consumption by scaling their total energy usage
+against the total time they were running, either in the background or
 foreground, reveals more information, as shown in Table~\ref{table-rate}. Our
 results identify Facebook Messenger, Google+, and the Super-Bright LED
 Flashlight as apps that rapidly-consume energy, while the Bank of America and
 Weather Channel apps consume energy slowly. Differences between apps in
 similar categories may begin to identify apps with problematic energy
 consumption, such as contrasting the high energy usage of Facebook Messenger
-with other messaging clients such as WhatsApp, Twitter, and Android Messaging.
+with other messaging clients such as WhatsApp, Twitter, and Android
+Messaging.
 \subsection{Foreground Energy Efficiency}
-Consumption rate alone, however, is insufficient to answer important
-questions about how efficient smartphone apps are. Youtube, for example, may
-consume a great deal of energy either because it is poorly written, or
-because it is delivering a great deal of content. Given the observations
-about background usage presented earlier, we were interested in using an apps
-foreground time as a utility metric to compute energy efficiency. In this
-conceptual framework, smartphone apps deliver utility through screen time
-with users, and should consume energy in proportion to the amount of time
-users spend actively interacting with them.
+Isolating the foreground component of execution time provides a better
+measure of value, since it ignores the time that users spend ignoring apps.
+Table~\ref{table-foreground} shows a measure of energy efficiency computed by
+utilizing foreground time alone as our value measure. Some surprising changes
+from the power results can be seen. Some apps have remaining in their former
+categories: Bank of America, which was identified as a low-power app, is also
+a highly-efficient app when using foreground time as the value measure; and
+Facebook Messenger, which was identified as a high-power app, is also marked
+as inefficient. Other apps, however, have switched categories. ESPN
+Sportscenter and Yahoo Mail do not consume much power, but also don't spend
+much time in the foreground; interestingly, none of the high-power apps
+looked better when their foreground usage was considered.
 \subsection{Content Energy Efficiency}
+Finally, we the data we collected by instrumenting the
+\texttt{SurfaceFlinger} and \texttt{AudioFlinger} components to compute a
+simple measure of content delivery. We measure the audio and video frame
+rates and combine them into a single measure by using bitrates corresponding
+to a 30~fps YouTube-encoded video and 128~kbps two-channel audio, with the
+weights representing the fact that a single frame of video contains much more
+content than a single sample of audio. We use this combined metric as the
+value measure and again use it to weight the energy consumption of each app,
+with the results shown in Table~\ref{table-content}.
+
+Comparing with the foreground energy efficiency again shows several
+interesting changes. Yahoo Mail, which foreground energy efficiency marked as
+inefficiency, looks more efficient when content delivery is considered. While
+it is possible that one \PhoneLab{} participant uses it to read email very
+quickly, it may be more likely that it uses a ``spinner'' or other fancy UI
+elements that generate artificially high frame rates without delivering much
+information. The inability to distinguish between meaningless and meaningful
+video frame content is a significant weakness of this simple approach.
+YouTube and Candy Crush Saga both earn high marks, which is encouraging given
+that they are very different apps but also might be a result of overweighting
+screen refreshes. The Android Clock is also an unsurprising result, as it
+requires almost no energy to generate a relatively-large number of screen
+redraws.
+
+\subsection{Survey Results and Discussion}
 \begin{figure*}[t]
 \centering