Man page 9 : check_asym_packing

check_asym_packing - Check to see if the group is packed into the sched doman.

int check_asym_packing(struct lb_env *  env , struct sd_lb_stats *  sds );

env
    The load balancing environment.

sds
    Statistics of the sched_domain which is to be packed

This is primarily intended to used at the sibling level. Some cores like POWER7 prefer to use lower numbered SMT threads. In the case of POWER7, it can move to lower SMT modes only when higher threads are idle. When in lower SMT modes, the threads will perform better since they share less core resources. Hence when we have idle threads, we want them to be the higher ones.

This packing function is run on idle threads. It checks to see if the busiest CPU in this domain (core in the P7 case) has a higher CPU number than the packing function is being run on. Here we are assuming lower CPU number will be equivalent to lower a SMT thread number.

Returns 1 when packing is required and a task should be moved to this CPU. The amount of the imbalance is returned in *imbalance.