Michael Ellerman [off-list ref] a écrit :

Christophe Leroy [off-list ref] writes:

quoted

This is copied and adapted from commit 5c929885f1bb ("powerpc/vdso64:
Add support for CLOCK_{REALTIME/MONOTONIC}_COARSE")
from Santosh Sivaraj [off-list ref]

Benchmark from vdsotest-all:
clock-gettime-realtime: syscall: 3601 nsec/call
clock-gettime-realtime:    libc: 1072 nsec/call
clock-gettime-realtime:    vdso: 931 nsec/call
clock-gettime-monotonic: syscall: 4034 nsec/call
clock-gettime-monotonic:    libc: 1213 nsec/call
clock-gettime-monotonic:    vdso: 1076 nsec/call
clock-gettime-realtime-coarse: syscall: 2722 nsec/call
clock-gettime-realtime-coarse:    libc: 805 nsec/call
clock-gettime-realtime-coarse:    vdso: 668 nsec/call
clock-gettime-monotonic-coarse: syscall: 2949 nsec/call
clock-gettime-monotonic-coarse:    libc: 882 nsec/call
clock-gettime-monotonic-coarse:    vdso: 745 nsec/call

Additional test passed with:
	vdsotest -d 30 clock-gettime-monotonic-coarse verify

This broke on 64-bit big endian, which uses the 32-bit VDSO, with errors
like:

  clock-gettime-monotonic-coarse/verify: 10 failures/inconsistencies  
encountered
  timestamp obtained from libc/vDSO not normalized:
  	[-1574202155, 1061008673]
  timestamp obtained from libc/vDSO predates timestamp
  previously obtained from kernel:
  	[74, 261310747] (kernel)
  	[-1574202155, 1061008673] (vDSO)
  timestamp obtained from libc/vDSO not normalized:
  	[-1574202155, 1061008673]
  timestamp obtained from libc/vDSO predates timestamp
  previously obtained from kernel:
  	[74, 261310747] (kernel)
  	[-1574202155, 1061008673] (vDSO)
  timestamp obtained from libc/vDSO not normalized:
  	[-1574202155, 1061008673]
  timestamp obtained from libc/vDSO predates timestamp
  previously obtained from kernel:
  	[74, 261310747] (kernel)
  	[-1574202155, 1061008673] (vDSO)
  timestamp obtained from libc/vDSO not normalized:
  	[-1574202155, 1061008673]
  timestamp obtained from libc/vDSO predates timestamp
  previously obtained from kernel:
  	[74, 261310747] (kernel)
  	[-1574202155, 1061008673] (vDSO)
  timestamp obtained from libc/vDSO not normalized:
  	[-1574202155, 1061008673]
  timestamp obtained from libc/vDSO predates timestamp
  previously obtained from kernel:
  	[74, 261310747] (kernel)
  	[-1574202155, 1061008673] (vDSO)
  Failure threshold (10) reached; stopping test.


The diff below seems to fix it, but I'm not sure it's correct. ie. we
just ignore the top part of the values, how does that work?

Your change makes sense, it is consistent with other functions using  
STAMP_XTIME.

It works because nanoseconds are max 999999999, it fits 32 bits regs.

Christophe