Created attachment 128869 [details]
CPU Usage hovering Start Center

Created attachment 128870 [details]
LLDB Backtrace

Version: 5.3.0.0.alpha1+
Build ID: 074f0ab1d76f16fe92493868e2f2de75e67792ef
CPU Threads: 4; OS Version: Mac OS X 10.12.1; UI Render: default; Layout Engine: new; 
TinderBox: MacOSX-x86_64@49-TDF, Branch:master, Time: 2016-11-15_00:29:07
Locale: en-US (en_US.UTF-8); Calc: group

LLDB debug information contains a warning:
@"WARNING: nextEventMatchingMask should only be called from the Main Thread! This will throw an exception in the future."

Within the backtrace I noticed:
- @"AppKit cannot convert carbon event class '%.4s' to CGEventRef."
- @"AppKit cannot convert carbon mouse event of kind '%ld' to CGEventRef."
- @"AppKit cannot convert carbon mouse events of button '%ld' to CGEventRef."
- @"WARNING: nextEventMatchingMask should only be called from the Main Thread! This will throw an exception in the future."
- THE_PROCESS_HAS_FORKED_AND_YOU_CANNOT_USE_THIS_COREFOUNDATION_FUNCTIONALITY___YOU_MUST_EXEC__

Confirming with

Version: 5.3.0.0.alpha1+
Build ID: e1af58c1260f442c2731ae8a705deba732246b1d
CPU Threads: 2; OS Version: Mac OS X 10.12.1; UI Render: default; Layout Engine: new; 
Locale: fr-FR (fr_FR.UTF-8); Calc: group

I don't see a hike as great as you indicate, but if one hovers the mouse over each icon in turn at approximately half a second per icon, processor usage shoots up to about 15% - still a performance problem though, as the app should be idling at around 0,2-0,5 %


I also noted that the first time after app launch that you click on the Template icon arrow to display the dropdown list, processor usage spikes to nearly 100% and remains there until the mouse moves over another icon.

A more complete list of possible causes:

CoreFoundation`_CFXNotificationPost:
@"*** attempt to post distributed notification '%s' thwarted by sandboxing.%s%s"\
__THE_PROCESS_HAS_FORKED_AND_YOU_CANNOT_USE_THIS_COREFOUNDATION_FUNCTIONALITY___YOU_MUST_EXEC__\

CoreFoundation`__CFRunLoopRun:\
"Unable to get port for run loop mode queue (%d)"\

CoreFoundation`CFRunLoopRunSpecific:
__THE_PROCESS_HAS_FORKED_AND_YOU_CANNOT_USE_THIS_COREFOUNDATION_FUNCTIONALITY___YOU_MUST_EXEC__\

AppKit`_DPSNextEvent:\
@"still in loop, timeout = %f seconds"\
@"got apple event of class %lx, ID %x"\
@"<Unknown Function>"\
@"<Unknown File>"\
@"Could not alloc empty CGEvent"\
@"AppKit cannot convert carbon event class '%.4s' to CGEventRef."\
@"AppKit cannot convert carbon mouse event of kind '%ld' to CGEventRef."\
@"AppKit cannot convert carbon mouse events of button '%ld' to CGEventRef."\
@"got unrecognized event, eventClass is %x, eventKind is %d"\
@"found event in concurrent event queue, looping around to get it"\
@"Force event behavior:%d"\
@"Received event: %@"\

NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:]:\
@"WARNING: nextEventMatchingMask should only be called from the Main Thread! This will throw an exception in the future."\

AppKit`-[NSApplication run]:\
@"<Unknown File>"\
@"NSApp with wrong _running count"\
@"No Info.plist file in application bundle or no NSPrincipalClass in the Info.plist file, exiting"\
@"Unable to find class: %@, exiting"\
@"Unable to load storyboard file: %@, exiting"\
@"Initial Storyboard controller is neither a NSWindowController nor a NSViewController: %@, from %@"\
@"Unable to find class: %@, exiting"\
@"Unable to load storyboard file: %@, exiting"\
@"Unable to load nib file: %@, exiting"\
@"No DelegateClass specfied in info dictionary, exiting"\
@"No NSMainNibFile or NSMainStoryboardFile specified in info dictionary, exiting"\

libvcllo.dylib`ImplSVMainHook:\
@"%@/Library/Saved Application State/%s.savedState/restorecount.plist"\
@"%@/Library/Saved Application State/%s.savedState/restorecount.txt"\

Isn't a MacOS only issue. Windows is also affected.

Found in:
Version: 5.4.0.0.alpha0+
Build ID: 84f2ff67a7e404febf710b1dc7f66d06745c503f
CPU Threads: 4; OS Version: Windows 6.19; UI Render: GL; 
TinderBox: Win-x86@42, Branch:master, Time: 2016-12-09_23:20:01
Locale: nl-NL (nl_NL); Calc: CL

and in
Version: 5.0.0.5
Build ID: 1b1a90865e348b492231e1c451437d7a15bb262b
Locale: en-US (nl_NL)

but not in:
Versie: 4.4.6.3 
Build ID: e8938fd3328e95dcf59dd64e7facd2c7d67c704d
Locale: nl_NL

CPU increase is a bit lower though: around 8% (maybe system depended)

Created attachment 129642 [details]
Process Monitor Output LO5400

Process Monitor Output

@Buovjaga:
Would you take a look at the process monitor output. Seems LibO is search for a helpfile... QueryDirectory	C:\Program Files (x86)\LibreOfficeDev 5\help\en	NO SUCH FILE	Filter: en

Created attachment 129669 [details]
SAL_LOG=+TIMESTAMP+INFO,+WARN

SAL_LOG Launching and hovering over Start Center
Version: 5.4.0.0.alpha0+
Build ID: d538d3d84172a74dfe97d59a6d3daf9a45459cab
CPU Threads: 4; OS Version: Windows 6.19; UI Render: default; 
TinderBox: Win-x86@39, Branch:master, Time: 2016-12-14_00:28:59
Locale: nl-NL (nl_NL); Calc: CL

Bibisected with win 5.0 repo to range https://cgit.freedesktop.org/libreoffice/core/log/?qt=range&q=9b4abcd1c45a646a1ac9120fe1c489ba6bb44e95...e6e8a060ecc6e4fd51cfe88e00d841d546ed5915
Tobias Madl's timer, idle & scheduling work seems to be the cause.
Won't bother adding to CC as he has not committed anything since 2015.
Adding stuff to See also that mention 9b4abcd1c45a646a1ac9120fe1c489ba6bb44e95

No Repro
Version: 6.5.0.0.alpha0+ (x64)
Build ID: 42a1a1c6b91907f81e15066ffab219411f18c4db
CPU threads: 4; OS: Windows 6.3 Build 9600; UI render: default; VCL: win; 
Locale: nl-NL (nl_NL); UI-Language: en-US
Calc: CL