malloc: Optimize the number of arenas for better application performance

[Yang Yanchao <yangyanchao6@huawei.com>]

At Kunpeng920 platform, tpcc-mysql scores decreased by about 11.2% 
between glibc-2.36 and glibc2.28.
Comparing the code, I find that the two commits causes performance 
degradation.
11a02b035b46 (misc: Add __get_nprocs_sched)
97ba273b5057 (linux: __get_nprocs_sched: do not feed CPU_COUNT_S with 
garbage [BZ #28850])

These two patches modify the default behavior.
However, my machine is 96 cores and I have 91 cores bound.
It means that perhaps the current way of computing arenas is not optimal.
So I roll back some of the code submitted by 11a02b035(misc: Add 
__get_nprocs_sched).

---
  malloc/arena.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/malloc/arena.c b/malloc/arena.c
index 0a684a720d..a1ee7928d3 100644
--- a/malloc/arena.c
+++ b/malloc/arena.c
@@ -937,7 +937,7 @@ arena_get2 (size_t size, mstate avoid_arena)
              narenas_limit = mp_.arena_max;
            else if (narenas > mp_.arena_test)
              {
-              int n = __get_nprocs_sched ();
+              int n = __get_nprocs ();

                if (n >= 1)
                  narenas_limit = NARENAS_FROM_NCORES (n);
-- 
2.33.0