[Bug libc/24268] bench-ffsll performance degradation on glibc 2.29

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=24268

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |RESOLVED
         Resolution|---                         |INVALID

--- Comment #4 from Florian Weimer <fweimer at redhat dot com> ---
Thanks.  So there is really nothing left to fix here.  Increasing function
alignment in general seems rather wasteful.  I suspect this is rather a cache
line conflict or something like this, and the alignment just makes the code use
a different cache line.

We could add an IFUNC that eliminates the conditional branch on modern CPUs
with BMI2. But that would be basically a defeat device because no real binaries
will call ffsll, only benchmarks, because GCC will expand ffsll calls inline.

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