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From: Parth Shah <parth@linux.ibm.com>
To: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>,
	subhra mazumdar <subhra.mazumdar@oracle.com>,
	linux-kernel@vger.kernel.org, peterz@infradead.org,
	mingo@redhat.com, tglx@linutronix.de, steven.sistare@oracle.com,
	dhaval.giani@oracle.com, daniel.lezcano@linaro.org,
	vincent.guittot@linaro.org, viresh.kumar@linaro.org,
	mgorman@techsingularity.net
Subject: Re: [RFC PATCH 1/9] sched,cgroup: Add interface for latency-nice
Date: Fri, 6 Sep 2019 17:52:37 +0530
Message-ID: <c159f942-1c5b-6957-ca8f-ef9b0a64e26e@linux.ibm.com> (raw)
In-Reply-To: <87o8zz2gu3.fsf@arm.com>



On 9/5/19 3:41 PM, Patrick Bellasi wrote:
> 
> On Thu, Sep 05, 2019 at 07:15:34 +0100, Parth Shah wrote...
> 
>> On 9/4/19 11:02 PM, Tim Chen wrote:
>>> On 8/30/19 10:49 AM, subhra mazumdar wrote:
>>>> Add Cgroup interface for latency-nice. Each CPU Cgroup adds a new file
>>>> "latency-nice" which is shared by all the threads in that Cgroup.
>>>
>>>
>>> Subhra,
>>>
>>> Thanks for posting the patchset.  Having a latency nice hint
>>> is useful beyond idle load balancing.  I can think of other
>>> application scenarios, like scheduling batch machine learning AVX 512
>>> processes with latency sensitive processes.  AVX512 limits the frequency
>>> of the CPU and it is best to avoid latency sensitive task on the
>>> same core with AVX512.  So latency nice hint allows the scheduler
>>> to have a criteria to determine the latency sensitivity of a task
>>> and arrange latency sensitive tasks away from AVX512 tasks.
>>>
>>
>>
>> Hi Tim and Subhra,
>>
>> This patchset seems to be interesting for my TurboSched patches as well
>> where I try to pack jitter tasks on fewer cores to get higher Turbo Frequencies.
>> Well, the problem I face is that we sometime end up putting multiple jitter tasks on a core
>> running some latency sensitive application which may see performance degradation.
>> So my plan was to classify such tasks to be latency sensitive thereby hinting the load
>> balancer to not put tasks on such cores.
>>
>> TurboSched: https://lkml.org/lkml/2019/7/25/296
>>
>>> You configure the latency hint on a cgroup basis.
>>> But I think not all tasks in a cgroup necessarily have the same
>>> latency sensitivity.
>>>
>>> For example, I can see that cgroup can be applied on a per user basis,
>>> and the user could run different tasks that have different latency sensitivity.
>>> We may also need a way to configure latency sensitivity on a per task basis instead on
>>> a per cgroup basis.
>>>
>>
>> AFAIU, the problem defined above intersects with my patches as well where the interface
>> is required to classify the jitter tasks. I have already tried few methods like
>> syscall and cgroup to classify such tasks and maybe something like that can be adopted
>> with these patchset as well.
> 
> Agree, these two patchest are definitively overlapping in terms of
> mechanisms and APIs to expose to userspace. You to guys seems to target
> different goals but the general approach should be:
> 
>  - expose a single and abstract concept to user-space
>    latency-nice or latency-tolerant as PaulT proposed at OSPM
> 

I agree. Both the patchset tries to classify a tasks for some purpose for better latency.
TurboSched requires the classification of whether the task is jitter and should not be given
enough resources/frequency. This is a boolean value.
Whereas, latency-nice is a range. So does that mean that a max-latency-nice task is a jitter?

I was thinking of not doing jitter packing on a core occupying
min-latency-nice (i.e, latency sensitive) task (until there are other busier cores).

Given this, we can expose a single per-task attribute to the user by a syscall, right?

>  - map this concept in kernel-space to different kind of bias, both at
>    wakeup time and load-balance time, and use both for RT and CFS tasks.
> 
> That's my understanding at least ;)
> 
> I guess we will have interesting discussions at the upcoming LPC to
> figure out a solution fitting all needs.

Definitely.

> 
>> Thanks,
>> Parth
> 
> Best,
> Patrick
> 


  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 [this message]
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
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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