• Paul E. McKenney's avatar
    rcu: Bind grace-period kthreads to non-NO_HZ_FULL CPUs · c0f489d2
    Paul E. McKenney authored
    Binding the grace-period kthreads to the timekeeping CPU resulted in
    significant performance decreases for some workloads.  For more detail,
    see:
    
    https://lkml.org/lkml/2014/6/3/395 for benchmark numbers
    
    https://lkml.org/lkml/2014/6/4/218 for CPU statistics
    
    It turns out that it is necessary to bind the grace-period kthreads
    to the timekeeping CPU only when all but CPU 0 is a nohz_full CPU
    on the one hand or if CONFIG_NO_HZ_FULL_SYSIDLE=y on the other.
    In other cases, it suffices to bind the grace-period kthreads to the
    set of non-nohz_full CPUs.
    
    This commit therefore creates a tick_nohz_not_full_mask that is the
    complement of tick_nohz_full_mask, and then binds the grace-period
    kthread to the set of CPUs indicated by this new mask, which covers
    the CONFIG_NO_HZ_FULL_SYSIDLE=n case.  The CONFIG_NO_HZ_FULL_SYSIDLE=y
    case still binds the grace-period kthreads to the timekeeping CPU.
    This commit also includes the tick_nohz_full_enabled() check suggested
    by Frederic Weisbecker.
    Reported-by: default avatarJet Chen <jet.chen@intel.com>
    Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
    [ paulmck: Created housekeeping_affine() and housekeeping_mask per
      fweisbec feedback. ]
    c0f489d2
tick-sched.c 29.6 KB