Hi Alex, On 02/24/2013 02:57 PM, Alex Shi wrote: > On 02/22/2013 04:54 PM, Peter Zijlstra wrote: >> On Thu, 2013-02-21 at 22:40 +0800, Alex Shi wrote: >>>> The name is a secondary issue, first you need to explain why you >>> think >>>> nr_running is a useful metric at all. >>>> >>>> You can have a high nr_running and a low utilization (a burst of >>>> wakeups, each waking a process that'll instantly go to sleep again), >>> or >>>> low nr_running and high utilization (a single process cpu bound >>>> process). >>> >>> It is true in periodic balance. But in fork/exec/waking timing, the >>> incoming processes usually need to do something before sleep again. >> >> You'd be surprised, there's a fair number of workloads that have >> negligible runtime on wakeup. > > will appreciate if you like introduce some workload. :) > BTW, do you has some idea to handle them? > Actually, if tasks is just like transitory, it is also hard to catch > them in balance, like 'cyclitest -t 100' on my 4 LCPU laptop, vmstat > just can catch 1 or 2 tasks very second. >> >>> I use nr_running to measure how the group busy, due to 3 reasons: >>> 1, the current performance policy doesn't use utilization too. >> >> We were planning to fix that now that its available. > > I had tried, but failed on aim9 benchmark. As a result I give up to use > utilization in performance balance. > Some trying and talking in the thread. > https://lkml.org/lkml/2013/1/6/96 > https://lkml.org/lkml/2013/1/22/662 >> >>> 2, the power policy don't care load weight. >> >> Then its broken, it should very much still care about weight. > > Here power policy just use nr_running as the criteria to check if it's > eligible for power aware balance. when do balancing the load weight is > still the key judgment. > >> >>> 3, I tested some benchmarks, kbuild/tbench/hackbench/aim7 etc, some >>> benchmark results looks clear bad when use utilization. if my memory >>> right, the hackbench/aim7 both looks bad. I had tried many ways to >>> engage utilization into this balance, like use utilization only, or >>> use >>> utilization * nr_running etc. but still can not find a way to recover >>> the lose. But with nr_running, the performance seems doesn't lose much >>> with power policy. >> >> You're failing to explain why utilization performs bad and you don't >> explain why nr_running is better. That things work simply isn't good > > Um, let me try to explain again, The utilisation need much time to > accumulate itself(345ms). Whenever with or without load weight, many > bursting tasks just give a minimum weight to the carrier CPU at the > first few ms. So, it is too easy to do a incorrect distribution here and > need migration on later periodic balancing.
I dont understand why forked tasks are taking time to accumulate the load.I understand this if it were to be a woken up task.The first time the forked task gets a chance to update the load itself,it needs to reflect full utilization.In __update_entity_runnable_avg both runnable_avg_period and runnable_avg_sum get equally incremented for a forked task since it is runnable.Hence where is the chance for the load to get incremented in steps? In sleeping tasks since runnable_avg_sum progresses much slower than runnable_avg_period,these tasks take much time to accumulate the load when they wake up.This makes sense of course.But how does this happen for forked tasks? Regards Preeti U Murthy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
