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clock_getres.2: Note circumstances in which "SMP" note applies. 

Reported-by: Rodrigo Campos <rodrigo@sdfg.com.ar>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2013-09-05 12:55:47 +02:00
parent 783d6cb454
commit 78638aae30
1 changed files with 14 additions and 4 deletions
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18
man2/clock_getres.2
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@ -221,12 +221,13 @@ are available.
(See also
.BR sysconf (3).)
.SH NOTES
.SS Note for SMP systems
The
.SS Historical note for SMP systems
Before Linux added kernel support for
.B CLOCK_PROCESS_CPUTIME_ID
and
.B CLOCK_THREAD_CPUTIME_ID
clocks are realized on many platforms using timers from the CPUs
.BR CLOCK_THREAD_CPUTIME_ID ,
glibc implemented these clocks on many platforms using timer
registers from the CPUs
(TSC on i386, AR.ITC on Itanium).
These registers may differ between CPUs and as a consequence
these clocks may return
@ -252,6 +253,15 @@ Glibc contains no provisions to deal with these offsets (unlike the Linux
Kernel).
Typically these offsets are small and therefore the effects may be
negligible in most cases.
Since glibc 2.4,
the wrapper functions for the system calls described in this page avoid
the abovementioned problems by employing the kernel implementation of
.B CLOCK_PROCESS_CPUTIME_ID
and
.BR CLOCK_THREAD_CPUTIME_ID ,
on systems that provide such an implementation
(i.e., Linux 2.6.12 and later).
.SH BUGS
According to POSIX.1-2001, a process with "appropriate privileges" may set the
.B CLOCK_PROCESS_CPUTIME_ID