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Author | SHA1 | Date |
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Lukasz Ziarek | 8087f16b8b | |
Lukasz Ziarek | 6897d0ddb7 |
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@ -79,7 +79,7 @@ Information on screen performance including framedrops came from the Android \te
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\paragraph{CPU Policies}
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We evaluate six different CPU policies under different workloads:
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We evaluate six different CPU policies:
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(i) the system default, \schedutil,
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(ii) a truncated \schedutil implemented by lower-bounding the CPU using the existing API discussed in subsection \ref{subsec:signal_perf_needs},
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(iii) a fixed 70\% speed using the existing \texttt{userspace} governor,
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@ -108,7 +108,7 @@ These workloads address evaluation claim (iii).
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\subsection{Screen Jank}
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\Cref{fig:jank_allapps} shows frame drop rates for the four workloads.
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\Cref{fig:jank_allapps} shows frame drop rates.
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These graphs address the performance aspect of claims (i) and (ii).
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On all workloads, \systemname and truncated \schedutil offer nearly identical or notably better performance than regular \schedutil.
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The Facebook load under \systemname costs an additional .3\%, or $\sim$.2 frames per second (12.6 frames per minute) at a 60fps display rate.
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@ -56,7 +56,7 @@ Armed with this knowledge, we realize the \systemname governor: a simple policy
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\paragraph{Case Studies}
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We studied a range of apps, including Facebook, Youtube, and Spotify.
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For each app, we developed a simple, short scripted interaction to study in terms of its performance characteristics and energy usage.
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For each app, we developed a short scripted interaction to study its performance characteristics and energy usage.
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We focus here primarily on the Facebook workload that we previously introduced in \Cref{sec:low-speed-in-practice}, and return to the other workloads to verify our findings in \Cref{sec:evaluation}.
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Our first goal is to understand what user-perceivable value this energy overhead obtains for us.
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@ -84,9 +84,7 @@ During this time, the user is waiting on the app to become responsive.
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It makes sense under such circumstances to run the CPUs at a higher speed to enhance user experience.
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Figure \ref{fig:coldstart_time_spot} shows the results of a study to examine the benefits and costs of doing this.
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Bear in mind that the unmodified system already uses the .. to provide a minimal $\sim$.5s boost to CPU speed.
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Ironically, the largest benefit comes in energy saved...
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@ -117,7 +115,7 @@ Even running the CPU at full speed, the system has more work.
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Adaptive widgets in mobile apps present an effectively infinite source of work to mobile CPUs over finite windows of interaction.
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}
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By adapting itself to the available CPU power, Facebook signals an effectively infinite source of work to the governor, which responds by ramping the CPU up to full speed.
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By adapting to the available CPU power, Facebook signals an effectively infinite source of work to the governor, which responds by ramping the CPU up to full speed.
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In this situation, speeds above $\fenergy$ may actually provide a perceptible benefit.
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However, even at the CPU's maximum frequency, more work is created than the CPU can keep up with.
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