[Bug libc/14438] New: clock_gettime CLOCK_THREAD_CPUTIME_ID doesn't delegate to vsyscall

["arun at sharma-home dot net" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=14438

             Bug #: 14438
           Summary: clock_gettime CLOCK_THREAD_CPUTIME_ID doesn't delegate
                    to vsyscall
           Product: glibc
           Version: 2.17
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
        AssignedTo: unassigned@sourceware.org
        ReportedBy: arun@sharma-home.net
                CC: drepper.fsp@gmail.com
    Classification: Unclassified


Created attachment 6566
  --> http://sourceware.org/bugzilla/attachment.cgi?id=6566
clock_gettime() makes syscalls, but __vdso_clock_gettime doesn't.

clock_gettime(CLOCK_THREAD_CPUTIME_ID, &ts) seems to always make a syscall,
even on kernels that provide a vdso. Although upstream kernels don't have the
patches we're running with, I find this behavior surprising.

Why doesn't glibc always call __vdso_clock_gettime() and let the kernel decide
on the best implementation regardless of the clock id?

Relevant patches:

http://thread.gmane.org/gmane.linux.kernel/1231015/focus=1231016

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