Public bug reported:

On this bug need litle explications function embedded
__compute_runnable_contrib have at beggining on "big" noop by 100 cycles
but why?

Looking bellow on contrib is added value but is not used for twice. 
2715                 /* Efficiently calculate \sum (1..n_period) 1024*y^i */
2716                 contrib = __compute_runnable_contrib(periods);
2717                 contrib = cap_scale(contrib, scale_freq);
2718                 if (weight) {

Look here :
http://lxr.free-electrons.com/source/kernel/sched/fair.c#L2716

And content of perf :

__compute_runnable_contrib  /proc/kcore                                         
                                 
       │
       │
       │
       │    Disassembly of section load0:
       │
       │    ffffffff810b2c70 <load0>:
100,00 │      nop
       │      cmp    $0x20,%rdi
       │    ↓ ja     13
       │      mov    -0x7e5e84c0(,%rdi,4),%eax
       │    ← retq
       │13:   cmp    $0x158,%rdi
       │    ↓ ja     27
       │      push   %rbp
       │      mov    %rsp,%rbp
       │      callq  0xffffffff810b2c10
       │      pop    %rbp
       │    ← retq
       │27:   mov    $0xba7e,%eax
       │    ← retq

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: linux-image-4.4.0-22-generic 4.4.0-22.40
ProcVersionSignature: Ubuntu 4.4.0-22.40-generic 4.4.8
Uname: Linux 4.4.0-22-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.1
Architecture: amd64
AudioDevicesInUse:
 USER        PID ACCESS COMMAND
 /dev/snd/pcmC0D0p:   asu        3213 F...m pulseaudio
 /dev/snd/controlC0:  asu        3213 F.... pulseaudio
CurrentDesktop: MATE
Date: Sat Jun 11 14:17:27 2016
InstallationDate: Installed on 2016-04-29 (42 days ago)
InstallationMedia: Ubuntu-Studio 16.04 LTS "Xenial Xerus" - Release amd64 
(20160420.1)
IwConfig:
 lo        no wireless extensions.
 
 enp1s0    no wireless extensions.
MachineType: Olidata S.p.A. ALABAMA
ProcFB: 0 inteldrmfb
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-4.4.0-22-generic 
root=/dev/mapper/192--168--0--108--vg-root ro
RelatedPackageVersions:
 linux-restricted-modules-4.4.0-22-generic N/A
 linux-backports-modules-4.4.0-22-generic  N/A
 linux-firmware                            1.157
RfKill:
 
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 07/08/2008
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: S0101
dmi.board.asset.tag: To Be Filled By O.E.M.
dmi.board.name: To be filled by O.E.M.
dmi.board.vendor: To be filled by O.E.M.
dmi.board.version: To be filled by O.E.M.
dmi.chassis.asset.tag: To Be Filled By O.E.M.
dmi.chassis.type: 3
dmi.chassis.vendor: To Be Filled By O.E.M.
dmi.chassis.version: To Be Filled By O.E.M.
dmi.modalias: 
dmi:bvnAmericanMegatrendsInc.:bvrS0101:bd07/08/2008:svnOlidataS.p.A.:pnALABAMA:pvrToBeFilledByO.E.M.:rvnTobefilledbyO.E.M.:rnTobefilledbyO.E.M.:rvrTobefilledbyO.E.M.:cvnToBeFilledByO.E.M.:ct3:cvrToBeFilledByO.E.M.:
dmi.product.name: ALABAMA
dmi.product.version: To Be Filled By O.E.M.
dmi.sys.vendor: Olidata S.p.A.

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: Confirmed


** Tags: amd64 apport-bug xenial

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https://bugs.launchpad.net/bugs/1591491

Title:
  On function __update_load_avg issue.

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