[PATCH] um: borrow bitops from the x86 tree

[Johannes Berg]

Hi Anton,

So I thought I'd test your performance patches here, and applied
(hopefully the latest versions of) on top of 5.9:

      um: allow the use of glibc functions instead of builtins
      um: Fetch registers only for signals which need them
      um: enable the use of optimized xor routines in UML
      um: add a UML specific futex implementation
      um: Remove use of asprinf in umid.c
      um: "borrow" atomics from x86 architecture
      um: "borrow" cmpxchg from x86 tree in UML
      um: borrow bitops from the x86 tree


With the patches (compiled with glibc functions), one of my trivial
virtual lab tests gets:

  Time (mean ± σ):     15.918 s ±  0.833 s    [User: 10.977 s, System: 5.600 s]
  Range (min … max):   15.371 s … 17.986 s    10 runs

It's not a large improvement, it seems noticable; without the patches I
get:

  Time (mean ± σ):     16.525 s ±  0.884 s    [User: 11.355 s, System: 5.648 s]
  Range (min … max):   15.682 s … 18.088 s    10 runs

johannes