From: Thara Gopinath <thara.gopinath@linaro.org>
To: Ionela Voinescu <ionela.voinescu@arm.com>
Cc: mingo@redhat.com, peterz@infradead.org,
vincent.guittot@linaro.org, rui.zhang@intel.com,
edubezval@gmail.com, qperret@google.com,
linux-kernel@vger.kernel.org, amit.kachhap@gmail.com,
javi.merino@kernel.org, daniel.lezcano@linaro.org
Subject: Re: [Patch v4 6/6] sched: thermal: Enable tuning of decay period
Date: Tue, 5 Nov 2019 15:26:06 -0500 [thread overview]
Message-ID: <5DC1DADE.60603@linaro.org> (raw)
In-Reply-To: <20191104161035.GA6680@e108754-lin>
On 11/04/2019 11:12 AM, Ionela Voinescu wrote:
> Hi Thara,
>
> On Tuesday 22 Oct 2019 at 16:34:25 (-0400), Thara Gopinath wrote:
>> Thermal pressure follows pelt signas which means the
>> decay period for thermal pressure is the default pelt
>> decay period. Depending on soc charecteristics and thermal
>> activity, it might be beneficial to decay thermal pressure
>> slower, but still in-tune with the pelt signals.
>
> I wonder if it can be beneficial to decay thermal pressure faster as
> well.
>
> This implementation makes 32 (LOAD_AVG_PERIOD) the minimum half-life
> of the thermal pressure samples. This results in more than 100ms for a
> sample to decay significantly and therefore let's say it can take more
> than 100ms for capacity to return to (close to) max when the CPU is no
> longer capped. This value seems high to me considering that a minimum
> value should result in close to 'instantaneous' behaviour, when there
> are thermal capping mechanisms that can react in ~20ms (hikey960 has a
> polling delay of 25ms, if I'm remembering correctly).
>
> I agree 32ms seems like a good default but given that you've made this
> configurable as to give users options, I'm wondering if it would be
> better to cover a wider range.
>
>> One way to achieve this is to provide a command line parameter
>> to set the decay coefficient to an integer between 0 and 10.
>>
>> Signed-off-by: Thara Gopinath <thara.gopinath@linaro.org>
>> ---
>> v3->v4:
>> - Removed the sysctl setting to tune decay period and instead
>> introduced a command line parameter to control it. The rationale
>> here being changing decay period of a PELT signal runtime can
>> result in a skewed average value for atleast some cycles.
>>
>> Documentation/admin-guide/kernel-parameters.txt | 5 +++++
>> kernel/sched/thermal.c | 25 ++++++++++++++++++++++++-
>> 2 files changed, 29 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>> index a84a83f..61d7baa 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -4273,6 +4273,11 @@
>> incurs a small amount of overhead in the scheduler
>> but is useful for debugging and performance tuning.
>>
>> + sched_thermal_decay_coeff=
>> + [KNL, SMP] Set decay coefficient for thermal pressure signal.
>> + Format: integer betweer 0 and 10
>> + Default is 0.
>> +
>> skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
>> xtime_lock contention on larger systems, and/or RCU lock
>> contention on all systems with CONFIG_MAXSMP set.
>> diff --git a/kernel/sched/thermal.c b/kernel/sched/thermal.c
>> index 0c84960..0da31e1 100644
>> --- a/kernel/sched/thermal.c
>> +++ b/kernel/sched/thermal.c
>> @@ -10,6 +10,28 @@
>> #include "pelt.h"
>> #include "thermal.h"
>>
>> +/**
>> + * By default the decay is the default pelt decay period.
>> + * The decay coefficient can change is decay period in
>> + * multiples of 32.
>
> This description has to be corrected as well, as per Peter's comment.
>
> Also, it might be good not to use the value 32 directly but to mention
> that the decay period is a shift of LOAD_AVG_PERIOD. If that changes,
> the translation from decay shift to decay period below will change as
> well.
Hi Ionela,
I sent out the v5 without fixing this. Even if there are no other
comments on v5 I will send out a v6 fixing this.
Regarding a slower decay, we need a strong case for it.
--
Warm Regards
Thara
next prev parent reply other threads:[~2019-11-05 20:26 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-22 20:34 [Patch v4 0/6] Introduce Thermal Pressure Thara Gopinath
2019-10-22 20:34 ` [Patch v4 1/6] sched/pelt.c: Add support to track thermal pressure Thara Gopinath
2019-10-31 9:47 ` Ionela Voinescu
2019-10-22 20:34 ` [Patch v4 2/6] sched: Add infrastructure to store and update instantaneous " Thara Gopinath
2019-10-28 15:21 ` Peter Zijlstra
2019-10-30 21:37 ` Thara Gopinath
2019-11-01 12:17 ` Dietmar Eggemann
2019-11-01 20:57 ` Thara Gopinath
2019-11-04 17:29 ` Dietmar Eggemann
2019-11-04 17:34 ` Vincent Guittot
2019-11-04 17:41 ` Dietmar Eggemann
2019-11-04 17:48 ` Vincent Guittot
2019-10-22 20:34 ` [Patch v4 3/6] sched/fair: Enable CFS periodic tick to update " Thara Gopinath
2019-10-28 15:24 ` Peter Zijlstra
2019-10-28 15:27 ` Peter Zijlstra
2019-10-30 21:41 ` Thara Gopinath
2019-10-31 16:11 ` Dietmar Eggemann
2019-10-31 16:46 ` Thara Gopinath
2019-10-22 20:34 ` [Patch v4 4/6] sched/fair: update cpu_capcity to reflect " Thara Gopinath
2019-10-23 12:28 ` Qais Yousef
2019-10-28 15:30 ` Peter Zijlstra
2019-10-31 10:53 ` Qais Yousef
2019-10-31 15:38 ` Dietmar Eggemann
2019-10-31 15:48 ` Vincent Guittot
2019-10-31 16:17 ` Dietmar Eggemann
2019-10-31 16:31 ` Vincent Guittot
2019-10-31 16:44 ` Dietmar Eggemann
2019-10-31 16:03 ` Thara Gopinath
2019-10-31 16:56 ` Qais Yousef
2019-10-22 20:34 ` [Patch v4 5/6] thermal/cpu-cooling: Update thermal pressure in case of a maximum frequency capping Thara Gopinath
2019-10-28 15:33 ` Peter Zijlstra
2019-10-31 16:29 ` Dietmar Eggemann
2019-10-31 16:38 ` Vincent Guittot
2019-11-01 15:47 ` Ionela Voinescu
2019-11-01 21:04 ` Thara Gopinath
2019-11-04 14:41 ` Ionela Voinescu
2019-10-31 16:46 ` Thara Gopinath
2019-10-22 20:34 ` [Patch v4 6/6] sched: thermal: Enable tuning of decay period Thara Gopinath
2019-10-28 15:42 ` Peter Zijlstra
2019-11-04 16:12 ` Ionela Voinescu
2019-11-05 20:26 ` Thara Gopinath [this message]
2019-11-05 21:29 ` Ionela Voinescu
2019-10-29 15:34 ` [Patch v4 0/6] Introduce Thermal Pressure Daniel Lezcano
2019-10-31 10:07 ` Ionela Voinescu
2019-10-31 11:54 ` Daniel Lezcano
2019-10-31 12:57 ` Ionela Voinescu
2019-10-31 17:48 ` Daniel Lezcano
2019-10-31 9:44 ` Ionela Voinescu
2019-10-31 16:41 ` Thara Gopinath
2019-10-31 16:52 ` Thara Gopinath
2019-11-05 21:04 ` Ionela Voinescu
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=5DC1DADE.60603@linaro.org \
--to=thara.gopinath@linaro.org \
--cc=amit.kachhap@gmail.com \
--cc=daniel.lezcano@linaro.org \
--cc=edubezval@gmail.com \
--cc=ionela.voinescu@arm.com \
--cc=javi.merino@kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=qperret@google.com \
--cc=rui.zhang@intel.com \
--cc=vincent.guittot@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
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).