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mobile measurements:the mobile app / OS perspective
Why understanding mobile app performance is hard
cellular performance matters to some apps
•most demanding apps• multiplayer gaming• VoIP• video chat
• somewhat demanding• web search• app interfaces with web services
• reasonably irrelevant• network transfers that aren’t in the critical path
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app development environment
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Start screen icons
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The Weather Channel
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MittRating
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Internet
Mitt Romney
MittRating
MittRating
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Internet
“Mitt Romney might vote for Obama as well”
“We recommend Mitt Romney for president”
“I would definitely trustMitt Romney with my money.”
“If I had a nickel for every time Mitt Romney said something stupid I'd be in his tax bracket”
Mitt Romney
MittRating
MittRating
Tweets
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Internet
“Mitt Romney might vote for Obama as well”
“We recommend Mitt Romney for president”
“I would definitely trustMitt Romney with my money.”
“If I had a nickel for every time Mitt Romney said something stupid I'd be in his tax bracket”
Mitt Romney
MittRating
MittRating
Tweets
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Internet
53%
“Mitt Romney might vote for Obama as well”
“We recommend Mitt Romney for president”
“I would definitely trustMitt Romney with my money.”
“If I had a nickel for every time Mitt Romney said something stupid I'd be in his tax bracket”
Mitt Romney
MittRating
MittRating
Tweets
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53%
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Hypothetical Synchronous Code
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ClickHandler() {
}
53%
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ClickHandler() {
tweets = HttpGet(url);
}
53%
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MittRating
Hypothetical Synchronous Code
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ClickHandler() {
tweets = HttpGet(url);rating = ProcessTweets(tweets);
}
ProcessTweets(tweets){
...}
53%
MittRating
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Hypothetical Synchronous Code
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ClickHandler() {
tweets = HttpGet(url);rating = ProcessTweets(tweets);display.Text = rating;
}
ProcessTweets(tweets){
...}
53%
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ClickHandler() {
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53%
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ClickHandler() {
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User Perceived Delay
53%
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Asynchronous Code
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ClickHandler() {
AsyncHttpGet(url, DownloadCallback);}DownloadCallback(tweets) {
rating = ProcessTweets(tweets);UIDispatch(DisplayRating, rating);
}DisplayRating(rating){
display.Text = rating;}ProcessTweets(tweets){
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Asynchronous Code
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ClickHandler() {
AsyncHttpGet(url, DownloadCallback);}DownloadCallback(tweets) {
rating = ProcessTweets(tweets);UIDispatch(DisplayRating, rating);
}DisplayRating(rating){
display.Text = rating;}ProcessTweets(tweets){
...} UI Thread
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53%
User Click
Asynchronous Code
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ClickHandler() {
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}DisplayRating(rating){
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53%
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Asynchronous Code
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ClickHandler() {
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53%
User Click
Asynchronous Code
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ClickHandler() {
AsyncHttpGet(url, DownloadCallback);}DownloadCallback(tweets) {
rating = ProcessTweets(tweets);UIDispatch(DisplayRating, rating);
}DisplayRating(rating){
display.Text = rating;}ProcessTweets(tweets){
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Apps are highly asynchronous
30 popular apps167,000 transactions from user study
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Apps are highly asynchronous
30 popular apps167,000 transactions from user study
• On average, 19 asynchronous calls per user transaction• On average, 8 parallel threads per user transaction
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Apps are highly asynchronous
For each user transaction, what was the critical path, and did the network matter?
30 popular apps167,000 transactions from user study
• On average, 19 asynchronous calls per user transaction• On average, 8 parallel threads per user transaction
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MittRating
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Tweets MittRatingMitt
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Tweets
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Tweets
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Tweets
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UI Thread
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User Transaction
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UI Thread
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User Click
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UI Thread
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User Transaction
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47%
User Click
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UI Thread
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Tweets
PostsTwitter
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User Click
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UI Thread
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DisplayUser Transaction
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PostsTwitter
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47%
User Click
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UI Thread
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Facebook Process Posts
Process Tweets
User Transaction Display26.March.2014 sharad.agarwal@microsoft.com 41
UI Thread
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Background Thread
Background Thread
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Fire
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Facebook Process Posts
Process Tweets
User Transaction Display26.March.2014 sharad.agarwal@microsoft.com 42
UI Thread
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Background Thread
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Facebook Process Posts
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Critical Path
User Transaction Display26.March.2014 sharad.agarwal@microsoft.com 43
UI Thread
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User Click
Thread WakeupThread Blocked
Fire
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Callback
Facebook Process Posts
Process Tweets
Critical PathOptimizing the critical path reduces the user perceived delay
User Transaction Display26.March.2014 sharad.agarwal@microsoft.com 44
UI Thread
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Background Thread
Background Thread
User Click
Thread WakeupThread Blocked
Fire
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Callback
Facebook Process Posts
Process Tweets
Critical PathOptimizing the critical path reduces the user perceived delay
User Transaction Display26.March.2014 sharad.agarwal@microsoft.com 45
key points
• app pages designed in GUI• async interfaces in code to UI elements• async interfaces to network• tendency to fetch many network objects at launch• fetch‐parse‐fetch pattern• critical path is hard to determine• in which user transactions does network matter?•of those, what caused network delay, if any?
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cellular network complicates this even more
• radio power states
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cellular network complicates this even more
• radio power states• latency varies by load
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cellular network complicates this even more
• radio power states• latency varies by load
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0
0.2
0.4
0.6
0.8
1
120 170 220
empi
rical
CD
F
RTT (ms)
cellular network complicates this even more
• radio power states• latency varies by load• latency varies
over space
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0
0.2
0.4
0.6
0.8
1
0 50 100 150 200
empi
rical
CD
F
RTT difference at 90th percentile (ms)
why am I telling you all this?•wireless BW, latency, RSSI, etc. data is useful for research
• relate it to user experience• this is hard because of how apps are built• need detailed & efficient app instrumentation
•our mobile OS throttles some network behavior• based on app performance need and cellular data limits• research systems to do this on a per app transfer basis, using detailed & lightweight instrumentation
•need detailed, predictive wireless performance info & how individual parts of apps are affected by net perf
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for more details
• cellular performance variations in short timescales• Switchboard paper in ACM MobiSys 2011
• asynchronous nature of apps & perf measurement• AppInsight paper in USENIX OSDI 2012
•network fetching behavior of apps• Procrastinator paper in ACM MobiSys 2014
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