From: Javi Merino <javi.merino@arm.com>
To: Leo Yan <leo.yan@linaro.org>
Cc: Eduardo Valentin <edubezval@gmail.com>,
Wei Xu <xuwei5@hisilicon.com>, Rob Herring <robh+dt@kernel.org>,
Pawel Moll <pawel.moll@arm.com>,
Mark Rutland <mark.rutland@arm.com>,
Ian Campbell <ijc+devicetree@hellion.org.uk>,
Kumar Gala <galak@codeaurora.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will.deacon@arm.com>,
Zhang Rui <rui.zhang@intel.com>,
kongxinwei <kong.kongxinwei@hisilicon.com>,
Punit Agrawal <Punit.Agrawal@arm.com>,
linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org
Subject: Re: [PATCH v2 1/5] thermal: change "hysteresis" as optional property
Date: Fri, 4 Mar 2016 11:57:53 +0000 [thread overview]
Message-ID: <20160304115752.GA13894@e104805> (raw)
In-Reply-To: <20160304030349.GA11012@leoy-linaro>
On Fri, Mar 04, 2016 at 11:03:49AM +0800, Leo Yan wrote:
> Hi Eduardo,
>
> On Thu, Mar 03, 2016 at 08:29:44AM -0800, Eduardo Valentin wrote:
> > Hi Leo,
> >
> > On Fri, Feb 26, 2016 at 11:43:43AM +0800, Leo Yan wrote:
> > > The property "hysteresis" is mandatory for trip points, so if without
> > > it the thermal zone cannot register successfully. But "hysteresis" is
> > > ignored in the thermal subsystem and only inquired by several thermal
> > > sensor drivers.
> >
> > I am not sure this a good direction to go. Remember that Linux
> > implementation not necessarily has to be the implication of the DT
> > binding. Hysteresis is a property that plays a significant role on
> > thermal control systems, which in many cases avoid overshooting cooling
> > actions. Having the DT writer to explicitly set it to 0 means that zone
> > does not suffer of overshooting and does not need hysteresis.
>
> After review current code, the "hysteresis" is used to calculate
> temperature falling threshold with a more conservative value; so that
> finally avoid overshooting issue.
>
> Please confirm if is my understanding correct or not?
>
> > If the Linux thermal subsystem has a problem with handling hysteresis, I
> > would rather fix Linux code than relaxing the DT binding. Or if you
> > still believe hysteresis is really optional, I would prefer to see a
> > better justification than "Linux ignores it".
I see it the other way round, Is hysteresis a property that, without
it, the thermal code can't configure itself so it fails to create the
trip point? The current code goes "There is no hysteresis for this
property, I don't know how to set up this trip point!". I think we
can do better than this.
> If we think about power allocator governor, PID's two parameters are
> also used to dismiss overshooting issue: one is k_po (proportional
> term), another is k_i (integral term). So that means after we apply
> power allocator governor, we don't need parameter "hysteresis" due PID
> algorithm can automatically dismiss potential errors.
I disagree. We shouldn't base DT decisions based on only one
governor in linux. Having said that, AFAICS all governors currently
ignore hysteresis.
Cheers,
Javi
next prev parent reply other threads:[~2016-03-04 11:57 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-26 3:43 [PATCH v2 0/5] thermal: hisilicon: enable power allocator for Hi6220 Leo Yan
2016-02-26 3:43 ` [PATCH v2 1/5] thermal: change "hysteresis" as optional property Leo Yan
[not found] ` <1456458227-12950-2-git-send-email-leo.yan-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
2016-03-03 10:45 ` Javi Merino
2016-03-03 16:29 ` Eduardo Valentin
2016-03-04 3:03 ` Leo Yan
2016-03-04 11:57 ` Javi Merino [this message]
2016-03-08 13:57 ` Leo Yan
2016-03-08 20:55 ` Eduardo Valentin
2016-03-09 11:10 ` Javi Merino
2016-03-20 15:40 ` Leo Yan
2016-02-26 3:43 ` [PATCH v2 2/5] thermal: hisilicon: support to use any sensor Leo Yan
2016-02-26 3:43 ` [PATCH v2 3/5] thermal: hisilicon: fix IRQ imbalance enabling Leo Yan
2016-02-26 3:43 ` [PATCH v2 4/5] arm64: dts: register Hi6220's thermal sensor Leo Yan
2016-02-26 3:43 ` [PATCH v2 5/5] arm64: dts: register Hi6220's thermal zone for power allocator Leo Yan
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=20160304115752.GA13894@e104805 \
--to=javi.merino@arm.com \
--cc=Punit.Agrawal@arm.com \
--cc=catalin.marinas@arm.com \
--cc=devicetree@vger.kernel.org \
--cc=edubezval@gmail.com \
--cc=galak@codeaurora.org \
--cc=ijc+devicetree@hellion.org.uk \
--cc=kong.kongxinwei@hisilicon.com \
--cc=leo.yan@linaro.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-pm@vger.kernel.org \
--cc=mark.rutland@arm.com \
--cc=pawel.moll@arm.com \
--cc=robh+dt@kernel.org \
--cc=rui.zhang@intel.com \
--cc=will.deacon@arm.com \
--cc=xuwei5@hisilicon.com \
/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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).