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[Bug libc/21305] clock_gettime(CLOCK_MONOTONIC_RAW) can and should use rdtsc instructions instead of entering kernel through VDSO


https://sourceware.org/bugzilla/show_bug.cgi?id=21305

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |WORKSFORME

--- Comment #6 from Florian Weimer <fweimer at redhat dot com> ---
(In reply to Jason Vas Dias from comment #5)
> So now I need to know : will a future version of glibc 
> ever consider providing an interface to rdtscp in user-space 
> for such platforms as my machine ?

I think you should propose a kernel patch which adds CLOCK_MONOTONIC_RAW
support first.  I doubt that for architectures which can use CPU clocks with
constant rates, there is a need for locking for CLOCK_MONOTONIC_RAW.  But Intel
engineers can probably help with that.

I don't think we will change glibc in the way you suggest because the vDSO data
structures appear to be kernel implementation details.  And there is the issue
that glibc should not have to know about specific TSC properties.

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