sched: Fix select_idle_sibling() bouncing cow syndrome
sched: Fix select_idle_sibling() bouncing cow syndrome

If the previous CPU is cache affine and idle, select it.

The current implementation simply traverses the sd_llc domain,
taking the first idle CPU encountered, which walks buddy pairs
hand in hand over the package, inflicting excruciating pain.

1 tbench pair (worst case) in a 10 core + SMT package:

  pre   15.22 MB/sec 1 procs
  post 252.01 MB/sec 1 procs

Signed-off-by: Mike Galbraith <bf687672b62c2181dfefd4771873b9307f539e64@online.de>
Cc: Peter Zijlstra <645ca7d3a8d3d4f60557176cd361ea8351edc32b@chello.nl>
Link: dca11908b81dc4c717e65b1a418af702a58d92c2@marge.simpson.net
Signed-off-by: Ingo Molnar <9dbbbf0688fedc85ad4da37637f1a64b8c718ee2@kernel.org>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs