On Tue, 2013-01-08 at 03:08 +0100, Frederic Weisbecker wrote:
> move_tasks() and active_load_balance_cpu_stop() both need
> to have the busiest rq clock uptodate because they may end
> up calling can_migrate_task() that uses rq->clock_task
> to determine if the task running in the busiest runqueue
> is cache hot.
>
> Hence if the busiest runqueue is tickless, update its clock
> before reading it.
>
> Signed-off-by: Frederic Weisbecker <fweis...@gmail.com>
> Cc: Alessio Igor Bogani <abog...@kernel.org>
> Cc: Andrew Morton <a...@linux-foundation.org>
> Cc: Chris Metcalf <cmetc...@tilera.com>
> Cc: Christoph Lameter <c...@linux.com>
> Cc: Geoff Levand <ge...@infradead.org>
> Cc: Gilad Ben Yossef <gi...@benyossef.com>
> Cc: Hakan Akkan <hakanak...@gmail.com>
> Cc: Ingo Molnar <mi...@kernel.org>
> Cc: Li Zhong <zh...@linux.vnet.ibm.com>
> Cc: Namhyung Kim <namhyung....@lge.com>
> Cc: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> Cc: Paul Gortmaker <paul.gortma...@windriver.com>
> Cc: Peter Zijlstra <pet...@infradead.org>
> Cc: Steven Rostedt <rost...@goodmis.org>
> Cc: Thomas Gleixner <t...@linutronix.de>
> [ Forward port conflicts ]
> Signed-off-by: Steven Rostedt <rost...@goodmis.org>
> ---
> kernel/sched/fair.c | 17 +++++++++++++++++
> 1 files changed, 17 insertions(+), 0 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 3d65ac7..e78d81104 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5002,6 +5002,7 @@ static int load_balance(int this_cpu, struct rq
> *this_rq,
> {
> int ld_moved, cur_ld_moved, active_balance = 0;
> int lb_iterations, max_lb_iterations;
> + int clock_updated;
> struct sched_group *group;
> struct rq *busiest;
> unsigned long flags;
> @@ -5045,6 +5046,7 @@ redo:
>
> ld_moved = 0;
> lb_iterations = 1;
> + clock_updated = 0;
> if (busiest->nr_running > 1) {
> /*
> * Attempt to move tasks. If find_busiest_group has found
> @@ -5068,6 +5070,14 @@ more_balance:
> */
> cur_ld_moved = move_tasks(&env);
> ld_moved += cur_ld_moved;
> +
> + /*
> + * Move tasks may end up calling can_migrate_task() which
> + * requires an uptodate value of the rq clock.
> + */
> + update_nohz_rq_clock(busiest);
> + clock_updated = 1;
According to the change log, it seems these lines should be added before
move_tasks() above?
Thanks, Zhong
> +
> double_rq_unlock(env.dst_rq, busiest);
> local_irq_restore(flags);
>
> @@ -5163,6 +5173,13 @@ more_balance:
> busiest->active_balance = 1;
> busiest->push_cpu = this_cpu;
> active_balance = 1;
> + /*
> + * active_load_balance_cpu_stop may end up
> calling
> + * can_migrate_task() which requires an uptodate
> + * value of the rq clock.
> + */
> + if (!clock_updated)
> + update_nohz_rq_clock(busiest);
> }
> raw_spin_unlock_irqrestore(&busiest->lock, flags);
>
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