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From: Valentin Schneider <valentin.schneider@arm.com>
To: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Subhra Mazumdar <subhra.mazumdar@oracle.com>,
	linux-kernel@vger.kernel.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,
	tim.c.chen@linux.intel.com, mgorman@techsingularity.net,
	parth@linux.ibm.com
Subject: Re: [RFC PATCH 1/9] sched,cgroup: Add interface for latency-nice
Date: Thu, 5 Sep 2019 15:48:56 +0100
Message-ID: <3d3306e4-3a78-5322-df69-7665cf01cc43@arm.com> (raw)
In-Reply-To: <87d0ge3n85.fsf@arm.com>

On 05/09/2019 14:07, Patrick Bellasi wrote:
> Yep, I think so fare we are all converging towards the idea to use the
> a signed range. Regarding the range itself, yes: 1024 looks very
> oversized, but +-20 is still something which leave room for a bit of
> flexibility and it also better matches the idea that we don't want to
> "enumerate behaviours" but just expose a knob. To map certain "bias" we
> could benefit from a slightly larger range.
> 
>> AFAICT this RFC only looks at wakeups, but I guess latency-nice can be
> 
> For the wakeup path there is also the TurboSched proposal by Parth:
> 
>    Message-ID: <20190725070857.6639-1-parth@linux.ibm.com> 
>    https://lore.kernel.org/lkml/20190725070857.6639-1-parth@linux.ibm.com/
> 
> we should keep in mind.
> 
>> applied elsewhere (e.g. load-balance, something like task_hot() and its
>> use of sysctl_sched_migration_cost).
> 
> For LB can you come up with some better description of what usages you
> see could benefit from a "per task" or "per task-group" latency niceness?
> 

task_hot() "ratelimits" migrations of tasks that were running up until
very recently (hence "cache hot"), but the knob is system wide. It might
make sense to exploit a per-task attribute to tune this (e.g. go wild if
not latency sensitive, otherwise stay away for longer).

We could perhaps even apply it to active load balance to similarly stay
away from latency sensitive tasks. Right now this is gated by a
sched_domain-wide attribute (nr_balance_failed). We could tweak this to
requiring more (less) failed attempts before interrupting latency (in)
sensitive tasks.

I'm sure we can come up with even more creative ways to pour even more
heuristics in there ;)

> 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
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 [this message]
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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