On Mon, Jan 25, 2021 at 02:02:58PM +0800, Aubrey Li wrote: > A long-tail load balance cost is observed on the newly idle path, > this is caused by a race window between the first nr_running check > of the busiest runqueue and its nr_running recheck in detach_tasks. > > Before the busiest runqueue is locked, the tasks on the busiest > runqueue could be pulled by other CPUs and nr_running of the busiest > runqueu becomes 1, this causes detach_tasks breaks with LBF_ALL_PINNED > flag set, and triggers load_balance redo at the same sched_domain level. > > In order to find the new busiest sched_group and CPU, load balance will > recompute and update the various load statistics, which eventually leads > to the long-tail load balance cost. > > This patch introduces a variable(sched_nr_lb_redo) to limit load balance > redo times, combined with sysctl_sched_nr_migrate, the max load balance > cost is reduced from 100+ us to 70+ us, measured on a 4s x86 system with > 192 logical CPUs. > > Cc: Andi Kleen <a...@linux.intel.com> > Cc: Tim Chen <tim.c.c...@linux.intel.com> > Cc: Srinivas Pandruvada <srinivas.pandruv...@linux.intel.com> > Cc: Rafael J. Wysocki <rafael.j.wyso...@intel.com> > Signed-off-by: Aubrey Li <aubrey...@linux.intel.com>
If redo_max is a constant, why is it not a #define instead of increasing the size of lb_env? -- Mel Gorman SUSE Labs
