skip shadow call when euid > 0 on linux

[atoomic]

maybe linux is not restrictive enough
and we could consider using a hint sh file
to enable it only on some specific distro?

[atoomic]

benchmark test file

[
 'getpwuid' =>
 {
  desc => "getpwuid",
  code => q[my @out = getpwuid(0);],
 },
 'getpwent' =>
 {
  desc => "getpwent",
  code => q[my @out = getpwent();],
 },
 'getpwnam' =>
 {
  desc => "getpwnam(root)",
  code => q[my @out = getpwnam('root');],
 },
]

[atoomic]

Run as root user

./perl -Ilib Porting/bench.pl --benchfile=/tmp/bench-getpw ../perl2/perl=blead ./perl=blead+patch
Key:
    Ir   Instruction read
    Dr   Data read
    Dw   Data write
    COND conditional branches
    IND  indirect branches
    _m   branch predict miss
    _m1  level 1 cache miss
    _mm  last cache (e.g. L3) miss
    -    indeterminate percentage (e.g. 1/0)

The numbers represent relative counts per loop iteration, compared to
blead at 100.0%.
Higher is better: for example, using half as many instructions gives 200%,
while using twice as many gives 50%.

getpwuid
getpwuid

        blead blead+patch
       ------ -----------
    Ir 100.00       99.92
    Dr 100.00       99.92
    Dw 100.00       99.93
  COND 100.00       99.94
   IND 100.00       98.99

COND_m 100.00      104.34
 IND_m 100.00       97.37

 Ir_m1 100.00       99.45
 Dr_m1 100.00      100.00
 Dw_m1 100.00      100.00

 Ir_mm 100.00      100.00
 Dr_mm 100.00      100.00
 Dw_mm 100.00      100.00

getpwent
getpwent

        blead blead+patch
       ------ -----------
    Ir 100.00       99.97
    Dr 100.00       99.97
    Dw 100.00       99.97
  COND 100.00       99.98
   IND 100.00       99.39

COND_m 100.00      100.57
 IND_m 100.00       97.29

 Ir_m1 100.00       99.95
 Dr_m1 100.00      110.53
 Dw_m1 100.00      100.00

 Ir_mm 100.00      100.00
 Dr_mm 100.00      100.00
 Dw_mm 100.00      100.00

getpwnam
getpwnam(root)

        blead blead+patch
       ------ -----------
    Ir 100.00       99.93
    Dr 100.00       99.92
    Dw 100.00       99.94
  COND 100.00       99.95
   IND 100.00       98.99

COND_m 100.00      102.59
 IND_m 100.00       97.37

 Ir_m1 100.00       99.95
 Dr_m1 100.00      100.00
 Dw_m1 100.00      100.00

 Ir_mm 100.00      100.00
 Dr_mm 100.00      100.00
 Dw_mm 100.00      100.00

AVERAGE

        blead blead+patch
       ------ -----------
    Ir 100.00       99.94
    Dr 100.00       99.94
    Dw 100.00       99.94
  COND 100.00       99.96
   IND 100.00       99.12

COND_m 100.00      102.48
 IND_m 100.00       97.34

 Ir_m1 100.00       99.79
 Dr_m1 100.00      103.28
 Dw_m1 100.00      100.00

 Ir_mm 100.00      100.00
 Dr_mm 100.00      100.00
 Dw_mm 100.00      100.00

[atoomic]

Run as non root user

./perl -Ilib Porting/bench.pl --benchfile=/tmp/bench-getpw ../perl2/perl=blead ./perl=blead+patch
Key:
    Ir   Instruction read
    Dr   Data read
    Dw   Data write
    COND conditional branches
    IND  indirect branches
    _m   branch predict miss
    _m1  level 1 cache miss
    _mm  last cache (e.g. L3) miss
    -    indeterminate percentage (e.g. 1/0)

The numbers represent relative counts per loop iteration, compared to
blead at 100.0%.
Higher is better: for example, using half as many instructions gives 200%,
while using twice as many gives 50%.

getpwuid
getpwuid

        blead blead+patch
       ------ -----------
    Ir 100.00      137.64
    Dr 100.00      130.24
    Dw 100.00      146.70
  COND 100.00      137.26
   IND 100.00      117.57

COND_m 100.00      211.55
 IND_m 100.00      117.24

 Ir_m1 100.00     1200.00
 Dr_m1 100.00      100.00
 Dw_m1 100.00      100.00

 Ir_mm 100.00      100.00
 Dr_mm 100.00      100.00
 Dw_mm 100.00      100.00

getpwent
getpwent

        blead blead+patch
       ------ -----------
    Ir 100.00      117.19
    Dr 100.00      117.45
    Dw 100.00      122.08
  COND 100.00      116.20
   IND 100.00      115.85

COND_m 100.00      123.67
 IND_m 100.00      114.08

 Ir_m1 100.00      717.86
 Dr_m1 100.00      130.00
 Dw_m1 100.00       33.33

 Ir_mm 100.00           -
 Dr_mm 100.00      100.00
 Dw_mm 100.00      100.00

getpwnam
getpwnam(root)

        blead blead+patch
       ------ -----------
    Ir 100.00      137.34
    Dr 100.00      129.98
    Dw 100.00      146.59
  COND 100.00      136.53
   IND 100.00      117.57

COND_m 100.00      211.11
 IND_m 100.00      117.24

 Ir_m1 100.00     1040.00
 Dr_m1 100.00      100.00
 Dw_m1 100.00      100.00

 Ir_mm 100.00      100.00
 Dr_mm 100.00      100.00
 Dw_mm 100.00      100.00

AVERAGE

        blead blead+patch
       ------ -----------
    Ir 100.00      129.99
    Dr 100.00      125.60
    Dw 100.00      137.43
  COND 100.00      129.22
   IND 100.00      116.99

COND_m 100.00      170.94
 IND_m 100.00      116.17

 Ir_m1 100.00      941.06
 Dr_m1 100.00      108.33
 Dw_m1 100.00       60.00

 Ir_mm 100.00      100.00
 Dr_mm 100.00      100.00
 Dw_mm 100.00      100.00

note blead=032639c40ae7d62f157b23237aae655d49115a56

[atoomic]

probably needs its own RT ticket to open a discussion about it

[khwilliamson]

Agreed that it needs RT