LKML Archive on lore.kernel.org
 help / color / Atom feed
From: Qais Yousef <qais.yousef@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Patrick Bellasi <patrick.bellasi@arm.com>,
	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 12:13:47 +0100
Message-ID: <20190905111346.2w6kuqrdvaqvgilu@e107158-lin.cambridge.arm.com> (raw)
In-Reply-To: <20190905104616.GD2332@hirez.programming.kicks-ass.net>

On 09/05/19 12:46, Peter Zijlstra wrote:
> On Thu, Sep 05, 2019 at 10:45:27AM +0100, Patrick Bellasi wrote:
> 
> > > From just reading the above, I would expect it to have the range
> > > [-20,19] just like normal nice. Apparently this is not so.
> > 
> > Regarding the range for the latency-nice values, I guess we have two
> > options:
> > 
> >   - [-20..19], which makes it similar to priorities
> >   downside: we quite likely end up with a kernel space representation
> >   which does not match the user-space one, e.g. look at
> >   task_struct::prio.
> > 
> >   - [0..1024], which makes it more similar to a "percentage"
> > 
> > Being latency-nice a new concept, we are not constrained by POSIX and
> > IMHO the [0..1024] scale is a better fit.
> > 
> > That will translate into:
> > 
> >   latency-nice=0 : default (current mainline) behaviour, all "biasing"
> >   policies are disabled and we wakeup up as fast as possible
> > 
> >   latency-nice=1024 : maximum niceness, where for example we can imaging
> >   to turn switch a CFS task to be SCHED_IDLE?
> 
> There's a few things wrong there; I really feel that if we call it nice,
> it should be like nice. Otherwise we should call it latency-bias and not
> have the association with nice to confuse people.
> 
> Secondly; the default should be in the middle of the range. Naturally
> this would be a signed range like nice [-(x+1),x] for some x. but if you
> want [0,1024], then the default really should be 512, but personally I
> like 0 better as a default, in which case we need negative numbers.
> 
> 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.

--
Qais Yousef

  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 [this message]
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20190905111346.2w6kuqrdvaqvgilu@e107158-lin.cambridge.arm.com \
    --to=qais.yousef@arm.com \
    --cc=daniel.lezcano@linaro.org \
    --cc=dhaval.giani@oracle.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mgorman@techsingularity.net \
    --cc=mingo@redhat.com \
    --cc=parth@linux.ibm.com \
    --cc=patrick.bellasi@arm.com \
    --cc=peterz@infradead.org \
    --cc=steven.sistare@oracle.com \
    --cc=subhra.mazumdar@oracle.com \
    --cc=tglx@linutronix.de \
    --cc=tim.c.chen@linux.intel.com \
    --cc=vincent.guittot@linaro.org \
    --cc=viresh.kumar@linaro.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
	git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git
	git clone --mirror https://lore.kernel.org/lkml/9 lkml/git/9.git
	git clone --mirror https://lore.kernel.org/lkml/10 lkml/git/10.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git