Useless operation on proc registry

[asu]

Exist one situation on 64bit linux-kernel on every fuction (i'fill angry) on perf exist
  16,67 │ mov %rsp,%rbp
which spent 16 cycles.
This move from offset pointer reg to base pointer register , looking here for more info
 http://eli.thegreenplace.net/2011/09/06/stack-frame-layout-on-x86-64/
 On 64 bit platform not need this.

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 4579 F...m pulseaudio
 /dev/snd/controlC0: asu 4579 F.... pulseaudio
CurrentDesktop: Unity
Date: Fri Jun 10 16:05:09 2016
InstallationDate: Installed on 2016-04-29 (41 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)]

this affect all functions from kernel can' t bee importance low ,on every invocation of all functions from kernel space ,from user space processor loose 16 cycles ( 16,67 │ mov %rsp,%rbp).
On user space not exist this issue.

[asu (corcodel-marian)]

Propose to change Importance:High

[asu (corcodel-marian)]

On terminal run sudo perf record -e cycles -ag and then perf report
iov_iter_init /proc/kcore
       │
       │
       │
       │ Disassembly of section load0:
       │
       │ ffffffff813fbae0 <load0>:
       │ push %rbp
       │ mov %gs:0x14204,%rax
       │ cmpq $0xffffffffffffffff,-0x3fe8(%rax)
100,00 │ mov %rsp,%rbp
       │ ↓ je 2f
       │ mov %esi,(%rdi)
       │ mov %rdx,0x18(%rdi)
       │1d: mov %rcx,0x20(%rdi)
       │ movq $0x0,0x8(%rdi)
       │ mov %r8,0x10(%rdi)
       │ pop %rbp
       │ ← retq
       │2f: or $0x2,%esi
       │ mov %rdx,0x18(%rdi)
       │ mov %esi,(%rdi)
       │ ↑ jmp 1d

Under function iov_iter_init loose 100 cycles!