From: Peter Zijlstra <peterz@infradead.org>
To: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: 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 13:40:30 +0200 [thread overview]
Message-ID: <20190905114030.GL2349@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <87imq72dpc.fsf@arm.com>
On Thu, Sep 05, 2019 at 12:18:55PM +0100, Patrick Bellasi wrote:
> Right, we have this dualism to deal with and current mainline behaviour
> is somehow in the middle.
>
> BTW, the FB requirement is the same we have in Android.
> We want some CFS tasks to have very small latency and a low chance
> to be preempted by the wake-up of less-important "background" tasks.
>
> I'm not totally against the usage of a signed range, but I'm thinking
> that since we are introducing a new (non POSIX) concept we can get the
> chance to make it more human friendly.
I'm arguing that signed _is_ more human friendly ;-)
> Give the two extremes above, would not be much simpler and intuitive to
> have 0 implementing the FB/Android (no latency) case and 1024 the
> (max latency) Oracle case?
See, I find the signed thing more natural, negative is a bias away from
latency sensitive, positive is a bias towards latency sensitive.
Also; 0 is a good default value ;-)
> Moreover, we will never match completely the nice semantic, give that
> a 1 nice unit has a proper math meaning, isn't something like 10% CPU
> usage change for each step?
Only because we were nice when implementing it. Posix leaves it
unspecified and we could change it at any time. The only real semantics
is a relative 'weight' (opengroup uses the term 'favourable').
> Could changing the name to "latency-tolerance" break the tie by marking
> its difference wrt prior/nice levels? AFAIR, that was also the original
> proposal [1] by PaulT during the OSPM discussion.
latency torrerance could still be a signed entity, positive would
signify we're more tolerant of latency (ie. less sensitive) while
negative would be less tolerant (ie. more sensitive).
> For latency-nice instead we will likely base our biasing strategies on
> some predefined (maybe system-wide configurable) const thresholds.
I'm not quite sure; yes, for some of these things, like the idle search
on wakeup, certainly. But say for wakeup-preemption, we could definitely
make it a task relative attribute.
next prev parent reply other threads:[~2019-09-05 11:40 UTC|newest]
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 [this message]
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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