Public bug reported:
Binary package hint: usplash
Progress bars should not bounce back and forward. The most obvious
example of this in Ubuntu is the start of the startup process of the
live CD, where the squashfs filesystem is being expanded. We can make
this feedback much smoother, without losing the main effect of the
bouncing, i.e. the reassurance that the system has not hung.
First, test the live CD startup on a representative sample of computers
to see how long the squashfs expansion takes on average, both as an
absolute measurement (T) and as a fraction of the total startup time
(F). Set these as constants in the usplash code. The fraction F can be
allocated to the squashfs step in the overall progress bar.
Then while the squashfs expansion is happening, usplash can smoothly
fill the progress bar asymptotically, so that by the average duration
(T) it has mostly but not completely reached F, slowing down smoothly so
that it never quite stops even if the expansion takes much longer than
usual.
Where
T is the average absolute time the expansion takes,
F is the average fraction of the overall startup time the expansion takes,
F/N is how much we want to allocate to reassuring movement if the expansion
takes longer than average, and
t is the current time,
a simple formula for this is
P = 1/F - F/(N^(t/T)).
As soon as the expansion step is finished, the progress bar should jump
straight to F. This will mean a little jump at the end, but that won't be
nearly as jarring as the bouncing was.
** Affects: usplash (Ubuntu)
Importance: Undecided
Assignee: Martin Pitt (pitti)
Status: New
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Live CD squashfs shouldn't cause bouncing progress bar
https://bugs.launchpad.net/bugs/319670
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