On function __update_load_avg issue.

[asu]

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.

[Brad Figg (brad-figg)]

This change was made by a bot.

[asu (corcodel-marian)]

Here need same like this

contrib = __compute_runnable_contrib(periods);
if (contrib)
      contrib;
contrib = cap_scale(contrib, scale_freq);
if (contrib)
     contrib += contrib;

[Joseph Salisbury (jsalisbury)]

This issue appears to be an upstream bug. Would it be possible for you to open an upstream bug report[0]? That will allow the upstream Developers to examine the issue, and may provide a quicker resolution to the bug.

Please follow the instructions on the wiki page[0]. The first step is to email the appropriate mailing list. If no response is received, then a bug may be opened on bugzilla.kernel.org.

Once this bug is reported upstream, please add the tag: 'kernel-bug-reported-upstream'.

[0] https://wiki.ubuntu.com/Bugs/Upstream/kernel