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Firefox OS/Performance/App Performance Validation: Difference between revisions
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, 1 February 2015Lakrits moved page FirefoxOS/Performance/App Performance Validation to Firefox OS/Performance/App Performance Validation: The official spelling of "Firefox OS" leaves a space between the two parts of the name. It's easier to find a page if the...
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'''Note: This page has now been edited published on MDN, as part of the App Center performance section — see https://developer.mozilla.org/en-US/Apps/Build/Performance/App_performance_validation. Any further changes should be made there. Talk to Chris Mills for more details.''' | |||
This page outlines a simple process for manually auditing and improving the performance of an app. | This page outlines a simple process for manually auditing and improving the performance of an app. | ||
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Debugging: | Debugging: | ||
* Attach with the App Manager and tweak the structure and styles of the page to trigger the desired behavior. | * Attach with the App Manager and tweak the structure and styles of the page to trigger the desired behavior. Positioning, z-index, and opacity styles are common culprits here. | ||
* Use dump-painting: https://wiki.mozilla.org/Gecko:DisplayListBasedInvalidation#Debugging_Invalidations_Problems (Example Displaylist: https://bug979026.bugzilla.mozilla.org/attachment.cgi?id=8396816) | |||
'''Report''': | |||
* Report as completed once all excessive painting is resolved. | |||
== 2. Reflows/Restyles == | == 2. Reflows/Restyles == | ||
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'''Verification Steps''': | '''Verification Steps''': | ||
* In the Developer menu -> Developer HUD, turn on the 'Jank' counter. | * In the Developer menu -> Developer HUD, turn on the 'Jank' counter. | ||
* Perform all common interactions with the app. Track the 'Jank' number for each of the interaction. When that number is above 10ms your app is | * Perform all common interactions with the app. Track the 'Jank' number for each of the interaction. When that number is above 10ms your app' scrolling is affected. Once that number is 100ms painting will fall behind and input will be delayed. 500ms+ indicate that this interaction will be noticeable jerky. | ||
* Understand the worse case responsiveness for each interaction of your app. Consider various workload for your app (like 5000 pictures). | * Understand the worse case responsiveness for each interaction of your app. Consider various workload for your app (like 5000 pictures in the Gallery App). | ||
'''Debugging''': | '''Debugging''': | ||
* Profile the app' main thread | * Profile the app' main thread. This is useful if you can't make an educated guess: https://developer.mozilla.org/en-US/docs/Performance/Profiling_with_the_Built-in_Profiler#Profiling_Boot_to_Gecko_%28with_a_real_device%29 | ||
* For | * For JavaScript related slowdown: Add function duration logging throughout the code. | ||
* Disable some functionality of your app to see if that reduces the event loop lag (jank). | * Disable some functionality of your app to see if that reduces the event loop lag (jank). | ||
'''Report''': | |||
* Report the numbers for various interaction and the workload used. | |||
== 4. Load Time == | == 4. Load Time == | ||
'''Platform Contact''': Varies, use profilers to narrow down the issue or contact the Performance team. | '''Platform Contact''': | ||
Varies, use profilers to narrow down the issue or contact the Performance team. | |||
'''What does it mean''': | |||
The duration, in millisecond, required to load the app. This is usually pretty difficult to measure because the definition of "load the app" varies from app to app. Generally though, we're talking about the time between the user launching the app and the '''visible''' UI being fully drawn and responsive. I put an emphasis on the visible UI because many apps require lots of computation and/or I/O to initialize their state enough to draw the full UI for the initial app screen. If every app waited until it was fully initialized before drawing the UI, they would all appear to be very slow and unresponsive. | |||
''' | The trick to getting a fast load time is to do as little as possible before putting up the '''visible''' part of the UI. All long term calculations and I/O should be delayed into an idle timer callback if possible. Apps that load to list UIs (e.g. contacts, sms, email) should only load enough data to display the UI that is initially visible to the user. The rest of the list can then be loaded in an idle timer callback. | ||
The real key here is to make sure that the UI is drawn as early as possible. Preferably, show a UI that isn't going to have a lot of box size re-adjustments due to reflows. Having a bunch of box resizes during load makes the app feel like web page rather than a native app. The goal here is to provide a native app experience using web technologies. | |||
'''Verification Steps''': | '''Verification Steps''': | ||
The easiest way to verify this is to use the existing profiler: [https://developer.mozilla.org/en-US/docs/Performance/Profiling_with_the_Built-in_Profiler#Profiling_Boot_to_Gecko_%28with_a_real_device%29] Since there are no obvious markers in the profiles of where your app load ends, it will be up to you to either output data to the log or call a dummy function where the loading should be done and then find the function call in the profile. The latter method is tricky because of the asynchronous nature of the callbacks and the rendering code. It all comes down to knowing your app's code well and then spending time to do a careful examination of the profiles in the Cleopatra tool: [http://people.mozilla.org/~bgirard/cleopatra/] | |||
If you are working on a B2G app, the datazilla tool measures cold_load_time for each of those. That's a good place to start when see if there has been a regression: [https://datazilla.mozilla.org/b2g/?branch=master&device=hamachi&range=7&test=cold_load_time&app_list=browser,calendar,camera,clock,contacts,email%20FTU,fm_radio,gallery,messages,music,phone,settings,template,usage,video&app=phone&gaia_rev=8f37a3795a07cfd5&gecko_rev=1c18d06925f1faef&plot=avg] | |||
'''Report''': | |||
* Capture profiles using the build-in profiler. | |||
* Upload them to Cleopatra and put the Cleopatra url in the bug. | |||
* Contact the performance team if you're stuck. | |||
== 5. Layer Tree == | == 5. Layer Tree == | ||
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'''What does it mean''': | '''What does it mean''': | ||
Having a good layer tree means we can most changes without having to repaint the page. Think of a | Having a good layer tree means we can perform most changes without having to repaint the page. Think of a cartoon on the television like The Simpsons: Most cartoons will divide their scene into a few layer and will move the layers themselves instead of redrawing the scene for every frame of the cartoon. Using layers to perform animations means we can avoid redrawing the page every frame and can simple move these layers around. | ||
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'''Debugging''': | '''Debugging''': | ||
* Attach with the App Manager and tweak the structure and styles of the page to trigger the desired behavior. | * Attach with the App Manager and tweak the structure and styles of the page to trigger the desired behavior. | ||
and | |||
* Get a display list dump. Build b2g with 'export B2G_DUMP_PAINTING=1' in your .userconfig (note: if you have a debug build, you don't need this). Set the preference 'user_pref("layout.display-list.dump", true);'. | |||
* Look for the display list dump for the particularly process at the moment of interest. It will contains a list of display items and their mappings between layers and their original frames. | |||
'''Creating/Destroying layers''': | |||
Continuously creating and destroying layers can hurt performance. Setting the pref "layers.flash-borders" when layer borders are activated will add a fading animation to layer borders when layers are created. Immediately after a layer is created, it's border is black and then it fades into it's usual color (green for most layers) during a second or two. This can highlight counter-intuitive behaviors, such as elements being already "layerized" seeing their layer being destroyed and recreated after a style change (for example, an animated element that moves around and then fades to transparent currently gets its layer recreated at the start of its opacity transition). | |||
Beware that this triggers full-tilt compositing (The compositor will try to composite continuously at 60fps regardless of whether anything has changed on the screen). So while this can be useful to understand the layerization behavior in some cases, it should not be used while doing performance measurements. | |||
== 6. Checkerboarding == | == 6. Checkerboarding == | ||
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'''What does it mean''': | '''What does it mean''': | ||
NOTE: Ideally at this point this section is just a verification. If the over-invalidation, reflows & event loop responsiveness is good then checkerboarding should be minimal to none. | NOTE: Ideally at this point this section is just a verification. If the over-invalidation, reflows & event loop responsiveness is good then checkerboarding should be minimal to none. More [http://www.masonchang.com/blog/2014/3/2/wow-such-checkerboard in depth explanation] here. | ||
Checkerboarding is when the app fails to keep up with the panning happening in the main process. When this happens a solid background color will be shown temporary until the page catches up. | Checkerboarding is when the app fails to keep up with the panning happening in the main process. When this happens a solid background color will be shown temporary until the page catches up. | ||
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'''Platform Contact''': Memshrink | '''Platform Contact''': Memshrink | ||
'''What does it mean''': | '''What does it mean''': Check that memory consumption is not excessive. | ||
'''Verification Steps''': | '''Verification Steps''': | ||
* Use tools/get_about_memory.py to get a memory reports dump while the app is running -- both shortly after start-up, and after using the app for a while. | |||
* Load the dumps in about:memory in desktop Firefox. Check for any measurements that seem to be excessive, particularly "heap-unclassified". | |||
* If "heap-unclassified" is high, re-run tools/get_about_memory.py with a [https://wiki.mozilla.org/Performance/MemShrink/DMD DMD-enabled] build, which will produce data that can be used to understand where additional memory reporters need to be added. | |||
== 9. Profiling == | == 9. Profiling == | ||
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'''What does it mean''': | '''What does it mean''': | ||
Power usage for a given change is difficult to measure. Power usage is directly correlated with CPU usage, and also with the use of various hardware features of the phone. | |||
'''Verification Steps''': | '''Verification Steps''': | ||
If you have a power harness available to you, you can do before and after power measurements by following the instructions on [https://developer.mozilla.org/en-US/Firefox_OS/Performance/Power this page]. If you don't have a power harness, please contact the performance team (#fxos-perf on IRC) for help. | |||