Messages in this thread | ![/](/images/icornerl.gif) | | Subject | Re: [RFC v5 4/6] sched/fair: Tune task wake-up logic to pack small background tasks on fewer cores | From | Parth Shah <> | Date | Wed, 9 Oct 2019 14:27:14 +0530 |
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On 10/8/19 10:22 PM, Dietmar Eggemann wrote: > [- Quentin Perret <quentin.perret@arm.com>] > [+ Quentin Perret <qperret@qperret.net>] > > See commit c193a3ffc282 ("mailmap: Update email address for Quentin Perret") >
noted. thanks for notifying me.
> On 07/10/2019 18:53, Parth Shah wrote: >> >> >> On 10/7/19 5:49 PM, Vincent Guittot wrote: >>> On Mon, 7 Oct 2019 at 10:31, Parth Shah <parth@linux.ibm.com> wrote: >>>> >>>> The algorithm finds the first non idle core in the system and tries to >>>> place a task in the idle CPU in the chosen core. To maintain >>>> cache hotness, work of finding non idle core starts from the prev_cpu, >>>> which also reduces task ping-pong behaviour inside of the core. >>>> >>>> Define a new method to select_non_idle_core which keep tracks of the idle >>>> and non-idle CPUs in the core and based on the heuristics determines if the >>>> core is sufficiently busy to place the incoming backgroung task. The >>>> heuristic further defines the non-idle CPU into either busy (>12.5% util) >>>> CPU and overutilized (>80% util) CPU. >>>> - The core containing more idle CPUs and no busy CPUs is not selected for >>>> packing >>>> - The core if contains more than 1 overutilized CPUs are exempted from >>>> task packing >>>> - Pack if there is atleast one busy CPU and overutilized CPUs count is <2 >>>> >>>> Value of 12.5% utilization for busy CPU gives sufficient heuristics for CPU >>>> doing enough work an > > [...] > >>>> @@ -6483,7 +6572,11 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f >>>> } else if (sd_flag & SD_BALANCE_WAKE) { /* XXX always ? */ >>>> /* Fast path */ >>>> >>>> - new_cpu = select_idle_sibling(p, prev_cpu, new_cpu); >>>> + if (is_turbosched_enabled() && unlikely(is_background_task(p))) >>>> + new_cpu = turbosched_select_non_idle_core(p, prev_cpu, >>>> + new_cpu); >>> >>> Could you add turbosched_select_non_idle_core() similarly to >>> find_energy_efficient_cpu() ? >>> Add it at the beg select_task_rq_fair() >>> Return immediately with theCPU if you have found one >>> Or let the normal path select a CPU if the >>> turbosched_select_non_idle_core() has not been able to find a suitable >>> CPU for packing >>> >> >> of course. I can do that. >> I was just not aware about the effect of wake_affine and so was waiting for >> such comments to be sure of. Thanks for this. >> Maybe I can add just below the sched_energy_present(){...} construct giving >> precedence to EAS? I'm asking this because I remember Patrick telling me to >> leverage task packing for android as well? > > I have a hard time imaging that Turbosched will be used in Android next > to EAS in the foreseeable future. > > First of all, EAS provides task packing already on Performance Domain > (PD) level (a.k.a. as cluster on traditional 2-cluster Arm/Arm64 > big.LITTLE or DynamIQ (with Phantom domains (out of tree solution)). > This is where we can safe energy without harming latency. > > See the tests results under '2.1 Energy test case' in > > https://lore.kernel.org/r/20181203095628.11858-1-quentin.perret@arm.com > > There are 10 to 50 small (classified solely by task utilization) tasks > per test case and EAS shows an effect on energy consumption by packing > them onto the PD (cluster) of the small CPUs. > > And second, the CPU supported topology is different to the one you're > testing on. >
cool. I was just keeping in mind the following quote " defining a generic spread-vs-pack wakeup policy which is something Android also could benefit from " (https://lkml.org/lkml/2019/6/28/628)
BTW, IIUC that does task consolidation only on single CPU unless rd->overload is set, right?
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