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From: Parth Shah <parth@linux.ibm.com>
To: Joel Fernandes <joel@joelfernandes.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Qais Yousef <qais.yousef@arm.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Patrick Bellasi <patrick.bellasi@arm.com>,
	Subhra Mazumdar <subhra.mazumdar@oracle.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@redhat.com>,
	Thomas Glexiner <tglx@linutronix.de>,
	steven.sistare@oracle.com, Dhaval Giani <dhaval.giani@oracle.com>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Tim Chen <tim.c.chen@linux.intel.com>,
	Mel Gorman <mgorman@techsingularity.net>
Subject: Re: [RFC PATCH 1/9] sched,cgroup: Add interface for latency-nice
Date: Mon, 20 Apr 2020 16:56:55 +0530
Message-ID: <7d4637c8-da8c-463d-30c6-a55c0a173316@linux.ibm.com> (raw)
In-Reply-To: <CAEXW_YTnS7Gz38Rw55M8q5NnJZJntOqxRHPC_AZ0uaQo+G4RqA@mail.gmail.com>

Hi Joel,

On 4/18/20 9:31 PM, Joel Fernandes wrote:
> Hi Dietmar,
> 
> On Thu, Apr 16, 2020 at 1:23 PM Dietmar Eggemann
> <dietmar.eggemann@arm.com> wrote:
>>
>> Hi Joel,
>>
>> On 16.04.20 02:02, Joel Fernandes wrote:
>>> On Thu, Sep 05, 2019 at 12:47:26PM +0100, Qais Yousef wrote:
>>>> On 09/05/19 13:30, Peter Zijlstra wrote:
>>>>> On Thu, Sep 05, 2019 at 12:13:47PM +0100, Qais Yousef wrote:
>>>>>> On 09/05/19 12:46, Peter Zijlstra wrote:
>>>>>
>>>>>>> This is important because we want to be able to bias towards less
>>>>>>> importance to (tail) latency as well as more importantance to (tail)
>>>>>>> latency.
>>>>>>>
>>>>>>> Specifically, Oracle wants to sacrifice (some) latency for throughput.
>>>>>>> Facebook OTOH seems to want to sacrifice (some) throughput for latency.
>>>>>>
>>>>>> Another use case I'm considering is using latency-nice to prefer an idle CPU if
>>>>>> latency-nice is set otherwise go for the most energy efficient CPU.
>>>>>>
>>>>>> Ie: sacrifice (some) energy for latency.
>>>>>>
>>>>>> The way I see interpreting latency-nice here as a binary switch. But
>>>>>> maybe we can use the range to select what (some) energy to sacrifice
>>>>>> mean here. Hmmm.
>>>>>
>>>>> It cannot be binary, per definition is must be ternary, that is, <0, ==0
>>>>> and >0 (or middle value if you're of that persuasion).
>>>>
>>>> I meant I want to use it as a binary.
>>>>
>>>>>
>>>>> In your case, I'm thinking you mean >0, we want to lower the latency.
>>>>
>>>> Yes. As long as there's an easy way to say: does this task care about latency
>>>> or not I'm good.
>>>
>>> Qais, Peter, all,
>>>
>>> For ChromeOS (my team), we are planning to use the upstream uclamp mechanism
>>> instead of the out-of-tree schedtune mechanism to provide EAS with the
>>> latency-sensitivity (binary/ternary) hint. ChromeOS is thankfully quite a bit
>>> upstream focussed :)
>>>
>>> However, uclamp is missing an attribute to provide this biasing to EAS as we
>>> know.
>>>
>>> What was the consensus on adding a per-task attribute to uclamp for providing
>>> this? Happy to collaborate on this front.
>>
>> We're planning to have a session about this topic (latency-nice
>> attribute per task group) during the virtual Pisa OSPM summit
>> retis.sssup.it/ospm-summit in May this year.
> 
> Cool, I registered as well.
> 
>>
>> There are two presentations/discussions planned:
>>
>> "Introducing Latency Nice for Scheduler Hints and Optimizing Scheduler
>> Task Wakeup" and "The latency nice use case for Energy-Aware-Scheduling
>> (EAS) in Android Common Kernel (ACK)"
>>
>> We'll probably merge those two into one presentation/discussion.
>>
>> So far we have Parth's per-task implementation
>>
>> https://lore.kernel.org/lkml/20200228090755.22829-1-parth@linux.ibm.com
> 
> Cool, I see it has some Reviewed-by tags so that's a good sign. Will
> look more into that.
> 
>> What's missing is the per-taskgroup implementation, at least from the
>> standpoint of ACK.
>>
>> The (mainline) EAS use-case for latency nice is already in ACK
>> (android-5.4):
>>
>> https://android.googlesource.com/kernel/common/+/760b82c9b88d2c8125abfc5f732cc3cd460b2a54
> 
> Yes, I was aware of this. But if we use task groups, then the
> transition from schedtune -> uclamp means now the tasks that use
> uclamp would also be subjected to cpu.shares. That's why we were
> looking into the per-task interface and glad there's some work on this
> already done.
> 

Yes, that series of latency_nice seems to be in good shape to be used for
any usecases. Hopefully, OSPM will lead to its upstreaming sooner :-)
But at the end, we aim to have both the per-task and cgroup based interface
to mark the latency_nice value of a task.
Till, then I'm finding some generic use-cases to show benefits of such task
attribute to increase community interest.


Thanks,
Parth


  reply index

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-30 17:49 [RFC PATCH 0/9] Task latency-nice subhra mazumdar
2019-08-30 17:49 ` [RFC PATCH 1/9] sched,cgroup: Add interface for latency-nice subhra mazumdar
2019-09-04 17:32   ` Tim Chen
2019-09-05  6:15     ` Parth Shah
2019-09-05 10:11       ` Patrick Bellasi
2019-09-06 12:22         ` Parth Shah
2019-09-05  8:31   ` Peter Zijlstra
2019-09-05  9:45     ` Patrick Bellasi
2019-09-05 10:46       ` Peter Zijlstra
2019-09-05 11:13         ` Qais Yousef
2019-09-05 11:30           ` Peter Zijlstra
2019-09-05 11:40             ` Patrick Bellasi
2019-09-05 11:48               ` Peter Zijlstra
2019-09-05 13:32                 ` Qais Yousef
2019-09-05 11:47             ` Qais Yousef
2020-04-16  0:02               ` Joel Fernandes
2020-04-16 17:23                 ` Dietmar Eggemann
2020-04-18 16:01                   ` Joel Fernandes
2020-04-20 11:26                     ` Parth Shah [this message]
2020-04-20 19:14                       ` Joel Fernandes
2020-04-20 11:47                     ` Qais Yousef
2020-04-20 19:10                       ` Joel Fernandes
2019-09-05 11:30           ` Patrick Bellasi
2019-09-05 11:47             ` Peter Zijlstra
2019-09-05 11:18         ` Patrick Bellasi
2019-09-05 11:40           ` Peter Zijlstra
2019-09-05 11:46             ` Patrick Bellasi
2019-09-05 11:46           ` Valentin Schneider
2019-09-05 13:07             ` Patrick Bellasi
2019-09-05 14:48               ` Valentin Schneider
2019-09-06 12:45               ` Parth Shah
2019-09-06 14:13                 ` Valentin Schneider
2019-09-06 14:32                   ` Vincent Guittot
2019-09-06 17:10                   ` Parth Shah
2019-09-06 22:50                     ` Valentin Schneider
2019-09-06 12:31       ` Parth Shah
2019-09-05 10:05   ` Patrick Bellasi
2019-09-05 10:48     ` Peter Zijlstra
2019-08-30 17:49 ` [RFC PATCH 2/9] sched: add search limit as per latency-nice subhra mazumdar
2019-09-05  6:22   ` Parth Shah
2019-08-30 17:49 ` [RFC PATCH 3/9] sched: add sched feature to disable idle core search subhra mazumdar
2019-09-05 10:17   ` Patrick Bellasi
2019-09-05 22:02     ` Subhra Mazumdar
2019-08-30 17:49 ` [RFC PATCH 4/9] sched: SIS_CORE " subhra mazumdar
2019-09-05 10:19   ` Patrick Bellasi
2019-08-30 17:49 ` [RFC PATCH 5/9] sched: Define macro for number of CPUs in core subhra mazumdar
2019-08-30 17:49 ` [RFC PATCH 6/9] x86/smpboot: Optimize cpumask_weight_sibling macro for x86 subhra mazumdar
2019-08-30 17:49 ` [RFC PATCH 7/9] sched: search SMT before LLC domain subhra mazumdar
2019-09-05  9:31   ` Peter Zijlstra
2019-09-05 20:40     ` Subhra Mazumdar
2019-08-30 17:49 ` [RFC PATCH 8/9] sched: introduce per-cpu var next_cpu to track search limit subhra mazumdar
2019-08-30 17:49 ` [RFC PATCH 9/9] sched: rotate the cpu search window for better spread subhra mazumdar
2019-09-05  6:37   ` Parth Shah
2019-09-05  5:55 ` [RFC PATCH 0/9] Task latency-nice Parth Shah
2019-09-05 10:31 ` Patrick Bellasi

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