Hi Yuyang, On 30 May 2016 at 21:48, Yuyang Du <yuyang...@intel.com> wrote: > On Mon, May 30, 2016 at 05:52:20PM +0200, Vincent Guittot wrote: >> The cfs_rq->avg.last_update_time is initialize to 0 with the main effect >> that the 1st sched_entity that will be attached, will keep its >> last_update_time set to 0 and will attached once again during the >> enqueue. >> Initialize cfs_rq->avg.last_update_time to 1 instead. >> >> Signed-off-by: Vincent Guittot <vincent.guit...@linaro.org> >> --- >> >> v3: >> - add initialization of load_last_update_time_copy for not 64bits system >> - move init into init_cfs_rq >> >> v2: >> - rq_clock_task(rq_of(cfs_rq)) can't be used because lock is not held >> >> kernel/sched/fair.c | 10 ++++++++++ >> 1 file changed, 10 insertions(+) >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index 218f8e8..86be9c1 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -8459,6 +8459,16 @@ void init_cfs_rq(struct cfs_rq *cfs_rq) >> cfs_rq->min_vruntime_copy = cfs_rq->min_vruntime; >> #endif >> #ifdef CONFIG_SMP >> + /* >> + * Set last_update_time to something different from 0 to make >> + * sure the 1st sched_entity will not be attached twice:once >> + * when attaching the task to the group and one more time when >> + * enqueueing the task. >> + */ > > The first time: "once when attaching the task to the group". > > That attaching is purely wrong, but will not have any effect (at least > load/util wise), because the task will later be inited in > init_entity_runnable_average().
This patch is not related to the init of a task but related to the init of the cfs_rq and to what happen with the 1st task that is enqueued on it. Lets take a task A that has already been scheduled on other cfs_rq so its se->avg.last_update_time is different from 0. Create a new task group TGB At creation, the cfs_rq->avg.last_update_time of this TGB is set to 0. Now move task A on TGB. A is attached to TGB so se->avg.last_update_time = cfs_rq->avg.last_update_time which is 0 A is then enqueued on th cfs_rq and because se->avg.last_update_time == 0, A will be attached one more time on the cfs_rq This patch set cfs_rq->avg.last_update_time to 1 at creation so the 1st time that A is attached to TGB, se->avg.last_update_time = cfs_rq->avg.last_update_time = 1 and A will not bve attached one more time during the enqueue. > > The second time: "one more time when enqueueing the task". > > In enqueue_entity_load_avg(), your patch will not have any effect either, > because of the above overwriting the new task's load in > init_entity_runnable_average(), no?
