2013/1/8 Li Zhong <[email protected]>:
> 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 <[email protected]>
>> Cc: Alessio Igor Bogani <[email protected]>
>> Cc: Andrew Morton <[email protected]>
>> Cc: Chris Metcalf <[email protected]>
>> Cc: Christoph Lameter <[email protected]>
>> Cc: Geoff Levand <[email protected]>
>> Cc: Gilad Ben Yossef <[email protected]>
>> Cc: Hakan Akkan <[email protected]>
>> Cc: Ingo Molnar <[email protected]>
>> Cc: Li Zhong <[email protected]>
>> Cc: Namhyung Kim <[email protected]>
>> Cc: Paul E. McKenney <[email protected]>
>> Cc: Paul Gortmaker <[email protected]>
>> Cc: Peter Zijlstra <[email protected]>
>> Cc: Steven Rostedt <[email protected]>
>> Cc: Thomas Gleixner <[email protected]>
>> [ Forward port conflicts ]
>> Signed-off-by: Steven Rostedt <[email protected]>
>> ---
>> 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?
Yeah, but eventually it seems that can_migrate_task() doesn't make use
of rq clock anymore. I guess I'll just drop that patch.
Thanks.