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SubjectRe: [PATCH] sched/fair: reduce preemption with IDLE tasks runable(Internet mail)
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On 12/08/2020 05:19, benbjiang(蒋彪) wrote:
> Hi,
>
>> On Aug 11, 2020, at 11:54 PM, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:
>>
>> On 11/08/2020 02:41, benbjiang(蒋彪) wrote:
>>> Hi,
>>>
>>>> On Aug 10, 2020, at 9:24 PM, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:
>>>>
>>>> On 06/08/2020 17:52, benbjiang(蒋彪) wrote:
>>>>> Hi,
>>>>>
>>>>>> On Aug 6, 2020, at 9:29 PM, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:
>>>>>>
>>>>>> On 03/08/2020 13:26, benbjiang(蒋彪) wrote:
>>>>>>>
>>>>>>>
>>>>>>>> On Aug 3, 2020, at 4:16 PM, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:
>>>>>>>>
>>>>>>>> On 01/08/2020 04:32, Jiang Biao wrote:
>>>>>>>>> From: Jiang Biao <benbjiang@tencent.com>

[...]

>> Trace a run of 2 SCHED_OTHER (nice 0) tasks and 1 SCHED_IDLE task on a
>> single CPU and trace_printk the conditions 'if (delta < 0)' and ' if
>> (delta > ideal_runtime)' in check_preempt_tick().
>>
>> Then do the same with 3 SCHED_OTHER (nice 0) tasks. You can also change
>> the niceness of the 2 SCHED_OTHER task to 19 to see some differences in
>> the kernelshark's task layout.
>>
>> rt-app (https://github.com/scheduler-tools/rt-app) is a nice tool to
>> craft those artificial use cases.
> With rt-app tool, sched_switch traced by ftrace, the result is as what I expected,

I use:

{
"tasks" : {
"task_other" : {
"instance" : 2,
"loop" : 200,
"policy" : "SCHED_OTHER",
"run" : 8000,
"timer" : { "ref" : "unique1" , "period" : 16000, "mode" : "absolute" },
"priority" : 0
},
"task_idle" : {
"instance" : 1,
"loop" : 200,
"policy" : "SCHED_IDLE",
"run" : 8000,
"timer" : { "ref" : "unique2" , "period" : 16000, "mode" : "absolute" }
}
},
"global" : {
"calibration" : 243, <-- Has to be calibrated against the CPU you run on !!!
"default_policy" : "SCHED_OTHER",
"duration" : -1
}
}

to have 2 (periodic) SCHED_OTHER and 1 SCHED_IDLE task.

> ** 2normal+1idle: idle preempt normal every 600+ms **

During the 3.2s the 2 SCHED_OTHER tasks run, the SCHED_IDLE task is
switched in only once, after ~2.5s.

> ** 3normal+idle: idle preempt normal every 1000+ms **

Ah, this was meant to be 3 SCHED_OTHER tasks only! To see the difference
in behavior.

> ** 2normal(nice 19)+1idle(nice 0): idle preempt normal every 30+ms **

During the 3.2s the 2 SCHED_OTHER tasks run, the SCHED_IDLE task is
switched in every ~45ms.

[...]

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