Messages in this thread | | | Subject | Re: [PATCH] sched/fair: Do not decay new task load on first enqueue | From | Dietmar Eggemann <> | Date | Wed, 28 Sep 2016 12:31:07 +0100 |
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On 28/09/16 12:19, Peter Zijlstra wrote: > On Wed, Sep 28, 2016 at 12:06:43PM +0100, Dietmar Eggemann wrote: >> On 28/09/16 11:14, Peter Zijlstra wrote: >>> On Fri, Sep 23, 2016 at 12:58:08PM +0100, Matt Fleming wrote:
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>> Not sure what you mean by 'after fixing' but the se is initialized with >> a possibly stale 'now' value in post_init_entity_util_avg()-> >> attach_entity_load_avg() before the clock is updated in >> activate_task()->enqueue_task(). > > I meant that after I fix the above issue of calling post_init with a > stale clock. So the + update_rq_clock(rq) in the patch.
OK.
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>>> While staring at this, I don't think we can still hit >>> vruntime_normalized() with a new task, so I _think_ we can remove that >>> !se->sum_exec_runtime clause there (and rejoice), no? >> >> I'm afraid that with accurate timing we will get the same situation that >> we add and subtract the same amount of load (probably 1024 now and not >> 1002 (or less)) to/from cfs_rq->runnable_load_avg for the initial (fork) >> hackbench run. >> After all, it's 'runnable' based. > > The idea was that since we now update rq clock before post_init and then > leave it be, both post_init and enqueue see the exact same timestamp, > and the delta is 0, resulting in no aging. > > Or did I fail to make that happen?
No, but IMHO what Matt wants is ageing for the hackench tasks at the end of their fork phase so there is a tiny amount of cfs_rq->runnable_load_avg left on cpuX after the fork related dequeue so the (load-based) fork-balancer chooses cpuY for the next hackbench task. That's why he wanted to avoid the __update_load_avg(se) on enqueue (thus adding 1024 to cfs_rq->runnable_load_avg) and do the ageing only on dequeue (removing <1024 from cfs_rq->runnable_load_avg).
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