Multiple issues are at play:
1) the regression seemingly observed in 
http://reqorts.qa.ubuntu.com/reports/qa/performance/dashboard/index.html turned 
out to be only a temporary blip. Subsequent runs show that there was no recent 
change in camera app startup time (on krillin).

2) the startup time measurement done in http://reqorts.qa.ubuntu.com/ is 
tricked by the way the camera app does things: it starts as fast as possible 
but once started shows a black screen for several seconds. It turns out that 
from a user perspective the camera app does not take 2.5s to startup on krillin 
but closer to 4.5s. Stopwatch measurements are as follows:
- krillin (363): 4.5s
- arale (356): 5s
- turbo (110): 7s

3) on turbo and I suspect some other devices or some other circumstances, the 
camera app startup is exceedingly high (over 7s) which I believe explains the 
reports we are getting here. After studying it I could not yet pinpoint the 
exact cause for such a slowdown. However I noticed that launching the camera 
app from the SDK made it start considerably faster, in 3s instead of 7s. After 
digging I came up with a small script that reproduces that speedup: 
http://pastebin.ubuntu.com/17696727/
Finally, I realised that simply having a "tail -f /var/log/syslog" opened while 
starting the camera app was enough to do the trick.
I investigated the possibility of CPU cores not being online in normal camera 
app startup thus possibly slowing it down but manually turning them on did not 
improve situation.

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Touch seeded packages, which is subscribed to camera-app in Ubuntu.
https://bugs.launchpad.net/bugs/1592447

Title:
  camera startup time regression

Status in Canonical System Image:
  In Progress
Status in camera-app package in Ubuntu:
  In Progress

Bug description:
  Please see 
  http://reqorts.qa.ubuntu.com/reports/qa/performance/dashboard/index.html

  the camera time recently jumped in startup time, but this did not seem
  to be something caused by a common component when comparing to other
  apps.

To manage notifications about this bug go to:
https://bugs.launchpad.net/canonical-devices-system-image/+bug/1592447/+subscriptions

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