In keyboard-shortcut-viewer, there are needs in the initialization process to layout all the label/views in StyledLabel [1,2]. This is time consuming.

[1] 
https://cs.chromium.org/chromium/src/ash/components/shortcut_viewer/views/keyboard_shortcut_view.cc?l=319&rcl=577ba3637231998f5f807afce564d7f417e7c2aa

[2]
https://cs.chromium.org/chromium/src/ash/components/shortcut_viewer/views/keyboard_shortcut_item_view.cc?l=172&rcl=92cbc6a3786d9e9e839cf9225672ad62064452aa
 

+msw FYI

To study the start-up time for keyboard-shortcut-viewer, we might need to separate the time of startup of the window itself and the time to init and layout the KeyboardShortcutItemListView [1] for all the Side tabs/categories. The layout of KeyboardShortcutItemListView is more time consuming because we dynamically calculate/generate labels in the StyledLabel, which probably is not an generic issue for other apps.

[1] 
https://cs.chromium.org/chromium/src/ash/components/shortcut_viewer/views/keyboard_shortcut_view.cc?l=301&rcl=577ba3637231998f5f807afce564d7f417e7c2aa

wutao, do you have a separate bug open for KSV init/layout performance?

I'd like to use this bug for general mojo app startup performance, and track the layout stuff separately.

I also wonder if we could speed things up by only laying out the first tab, then posting a task to do the layout for the tabs that aren't visible. I don't know if we do that or not. I guess it depends on where the time goes (like, if the time is due to font loading/rendering then layout won't matter as much).

jamescook@, we do not have separate bug open for KSV init/layout performance.
I tested to comment out lines 261 to 275 and the line 282 [1], the mus app version of KSH can start very quick. This indicates that the layout might be the major issue.
We did not do as you mentioned, only laying out the first tab and run other tab in the background, which could significantly speed up.


There are two bugs related to the layout performance. The first one has been fixed to reduce the search latency and enhance the search experience.

The second bug, has more performance requirement, we do not have Milestone target because KSH is not resizable by design.

1. Fixed. bug 818882: Reduce the latency in search mode of Keyboard Shortcut Viewer

2. The layout performance is the key concern, but debounce might work it around to avoid repeatedly layout: bug 822377: Layout needs to support resizing and maximizes

[1] https://cs.chromium.org/chromium/src/ash/components/shortcut_viewer/views/keyboard_shortcut_view.cc?rcl=577ba3637231998f5f807afce564d7f417e7c2aa&l=261

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d9b2272021c2954e304df95a1bc803454d08fb6d

commit d9b2272021c2954e304df95a1bc803454d08fb6d
Author: James Cook <jamescook@chromium.org>
Date: Mon Jun 04 21:13:59 2018

Don't use font service with aura mus

This improves keyboard shortcut viewer app startup time by 150 ms on
veyron_minnie (32-bit ARM).

Background:
The font service allows loading fonts from arbitrary paths (needed on
Linux) for sandboxing. However, it isn't necessary for mus apps,
since they launch as utility processes and can use fonts directly.
We can revisit this if we need tighter sandboxing for mus apps.

Bug:  847613 
Change-Id: I6e570d8e5483ed004cd815000d85f8ead5310b8c
Reviewed-on: https://chromium-review.googlesource.com/1085631
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#564240}
[modify] https://crrev.com/d9b2272021c2954e304df95a1bc803454d08fb6d/ui/views/mus/BUILD.gn
[modify] https://crrev.com/d9b2272021c2954e304df95a1bc803454d08fb6d/ui/views/mus/DEPS
[modify] https://crrev.com/d9b2272021c2954e304df95a1bc803454d08fb6d/ui/views/mus/aura_init.cc
[modify] https://crrev.com/d9b2272021c2954e304df95a1bc803454d08fb6d/ui/views/mus/aura_init.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/bb024f15dc64220cf50dc7ceb362ce273697fc12

commit bb024f15dc64220cf50dc7ceb362ce273697fc12
Author: James Cook <jamescook@chromium.org>
Date: Wed Jun 06 17:42:07 2018

chromeos: Add UMA metrics for keyboard shortcut viewer startup time

This will measure the time from Ctrl-Shift-/ keystroke to dialog show.
This CL works with the non-mojo-app shortcut viewer we're using today.
When we switch to the app version we'll need to pass the keystroke
time over mojo to the app, perhaps via a Toggle() method. Adding the
mojo Toggle() interface is tracked in  crbug.com/847615 

Metric is Keyboard.ShortcutViewer.StartupTime

Bug:  847615 ,  847613 
Test: added to ash_unittests, manually checked chrome://histograms
Change-Id: I425f44d0b71543f225d73857365d050be0e1b446
Reviewed-on: https://chromium-review.googlesource.com/1087779
Commit-Queue: James Cook <jamescook@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Tao Wu <wutao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#564952}
[modify] https://crrev.com/bb024f15dc64220cf50dc7ceb362ce273697fc12/ash/components/shortcut_viewer/BUILD.gn
[modify] https://crrev.com/bb024f15dc64220cf50dc7ceb362ce273697fc12/ash/components/shortcut_viewer/shortcut_viewer_application.cc
[modify] https://crrev.com/bb024f15dc64220cf50dc7ceb362ce273697fc12/ash/components/shortcut_viewer/shortcut_viewer_application.h
[modify] https://crrev.com/bb024f15dc64220cf50dc7ceb362ce273697fc12/ash/components/shortcut_viewer/views/keyboard_shortcut_view.cc
[modify] https://crrev.com/bb024f15dc64220cf50dc7ceb362ce273697fc12/ash/components/shortcut_viewer/views/keyboard_shortcut_view.h
[modify] https://crrev.com/bb024f15dc64220cf50dc7ceb362ce273697fc12/ash/components/shortcut_viewer/views/keyboard_shortcut_view_unittest.cc
[modify] https://crrev.com/bb024f15dc64220cf50dc7ceb362ce273697fc12/chrome/browser/ui/ash/ksv/keyboard_shortcut_viewer_util.cc
[modify] https://crrev.com/bb024f15dc64220cf50dc7ceb362ce273697fc12/tools/metrics/histograms/histograms.xml