Bug#956418: src:glibc: Please provide optimized builds for ARMv8.1

[Noah Meyerhans <noahm@debian.org>]

On Sat, Apr 11, 2020 at 10:23:54PM +0200, Florian Weimer wrote:
> Or put differently: If upstream doesn't want to default to
> -moutline-atomics, why should Debian?

Well, ultimately we own our build configurations and the optimizations
we enable therein.  If we don't want to enable -moutline-atomics
globally, then a second, optimized library is also an option.  IMO,
timing data like these should be enough to show that it's worth making a
change somewhere:

# 100 serial invocations of the "a.c" program attached to the bug
# report, linked against libc with -moutline-atomics
real    0m1.902s
user    0m3.488s
sys     0m25.498s

# 100 invocations of the same program linked against glibc with
# -march=armv8.1-a
real    0m1.844s
user    0m3.137s
sys     0m24.275s

# 100 invocations of the same program against our current libc build:
real    8m15.452s
user    130m33.139s
sys     0m1.162s

noah