from https://pubs.opengroup.org/onlinepubs/007904875/functions/setpriority.html:
1.The nice value shall in the range [-{NZERO},{NZERO} -1]
2.Lower nice value shall cause more favorable scheduling
Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>
Change-Id: I5ad60d92abc3b69fbaa406da68cec2e40ca3fa6d