All of lore.kernel.org
 help / color / mirror / Atom feed
From: Daniel Lezcano <daniel.lezcano@linaro.org>
To: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Cc: Rob Herring <robh+dt@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Russell King - ARM Linux <linux@armlinux.org.uk>,
	Maxime Coquelin <mcoquelin.stm32@gmail.com>,
	Alexandre Torgue <alexandre.torgue@st.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ludovic Barre <ludovic.barre@st.com>,
	Julien Thierry <julien.thierry@arm.com>,
	Sudeep Holla <sudeep.holla@arm.com>,
	Arnd Bergmann <arnd@arndb.de>,
	devicetree@vger.kernel.org,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v8 4/6] clocksource: stm32: only use 32 bits timers
Date: Fri, 8 Dec 2017 08:52:12 +0100	[thread overview]
Message-ID: <4f9ed3dd-cf02-eed7-7fdd-38f8dc092eee@linaro.org> (raw)
In-Reply-To: <CA+M3ks4KLy0VkJOSGR7tmefOT1rw9nrMsRQvwwK-YZQ7Gm7hQA@mail.gmail.com>

On 07/12/2017 21:36, Benjamin Gaignard wrote:
> 2017-12-07 17:49 GMT+01:00 Daniel Lezcano <daniel.lezcano@linaro.org>:
>> On 07/12/2017 17:33, Benjamin Gaignard wrote:
>>> 2017-12-07 16:27 GMT+01:00 Daniel Lezcano <daniel.lezcano@linaro.org>:
>>>> On 14/11/2017 09:52, Benjamin Gaignard wrote:
>>>>> The clock driving counters is at 90MHz so the maximum period
>>>>> for 16 bis counters is around 750 ms which is a short period
>>>>> for a clocksource.
>>>>
>>>> Isn't it 728us ?
>>>
>>> yes it is: 2^16 / 90.000.000 => 728us
>>
>> Ok, now I can do the connection with the previous patch.
>>
>> So, the real issue of all this is the 16bits clocksource is wrapping up
>> every 728us, hence the clockevent periodically expires every ~728us to
>> keep the timekeeping consistent. Unfortunately, the kernel has a too
>> high overhead for this as the system is consistently processing this
>> timer leading to a CPU time resource starvation.
>>
>> Is that correct ?
> 
> Yes that is correct

Oh man. That was unclear since the beginning, we are not talking about
inaccurate clocksource or whatever but just these 16bits timers can't
work on Linux.


-- 
 <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs

Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog

WARNING: multiple messages have this Message-ID (diff)
From: Daniel Lezcano <daniel.lezcano-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
To: Benjamin Gaignard
	<benjamin.gaignard-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
Cc: Rob Herring <robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>,
	Russell King - ARM Linux
	<linux-I+IVW8TIWO2tmTQ+vhA3Yw@public.gmane.org>,
	Maxime Coquelin
	<mcoquelin.stm32-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	Alexandre Torgue <alexandre.torgue-qxv4g6HH51o@public.gmane.org>,
	Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>,
	Ludovic Barre <ludovic.barre-qxv4g6HH51o@public.gmane.org>,
	Julien Thierry <julien.thierry-5wv7dgnIgG8@public.gmane.org>,
	Sudeep Holla <sudeep.holla-5wv7dgnIgG8@public.gmane.org>,
	Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>,
	devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	Linux ARM
	<linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org>,
	Linux Kernel Mailing List
	<linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
Subject: Re: [PATCH v8 4/6] clocksource: stm32: only use 32 bits timers
Date: Fri, 8 Dec 2017 08:52:12 +0100	[thread overview]
Message-ID: <4f9ed3dd-cf02-eed7-7fdd-38f8dc092eee@linaro.org> (raw)
In-Reply-To: <CA+M3ks4KLy0VkJOSGR7tmefOT1rw9nrMsRQvwwK-YZQ7Gm7hQA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>

On 07/12/2017 21:36, Benjamin Gaignard wrote:
> 2017-12-07 17:49 GMT+01:00 Daniel Lezcano <daniel.lezcano-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>:
>> On 07/12/2017 17:33, Benjamin Gaignard wrote:
>>> 2017-12-07 16:27 GMT+01:00 Daniel Lezcano <daniel.lezcano-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>:
>>>> On 14/11/2017 09:52, Benjamin Gaignard wrote:
>>>>> The clock driving counters is at 90MHz so the maximum period
>>>>> for 16 bis counters is around 750 ms which is a short period
>>>>> for a clocksource.
>>>>
>>>> Isn't it 728us ?
>>>
>>> yes it is: 2^16 / 90.000.000 => 728us
>>
>> Ok, now I can do the connection with the previous patch.
>>
>> So, the real issue of all this is the 16bits clocksource is wrapping up
>> every 728us, hence the clockevent periodically expires every ~728us to
>> keep the timekeeping consistent. Unfortunately, the kernel has a too
>> high overhead for this as the system is consistently processing this
>> timer leading to a CPU time resource starvation.
>>
>> Is that correct ?
> 
> Yes that is correct

Oh man. That was unclear since the beginning, we are not talking about
inaccurate clocksource or whatever but just these 16bits timers can't
work on Linux.


-- 
 <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs

Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog

--
To unsubscribe from this list: send the line "unsubscribe devicetree" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

WARNING: multiple messages have this Message-ID (diff)
From: daniel.lezcano@linaro.org (Daniel Lezcano)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v8 4/6] clocksource: stm32: only use 32 bits timers
Date: Fri, 8 Dec 2017 08:52:12 +0100	[thread overview]
Message-ID: <4f9ed3dd-cf02-eed7-7fdd-38f8dc092eee@linaro.org> (raw)
In-Reply-To: <CA+M3ks4KLy0VkJOSGR7tmefOT1rw9nrMsRQvwwK-YZQ7Gm7hQA@mail.gmail.com>

On 07/12/2017 21:36, Benjamin Gaignard wrote:
> 2017-12-07 17:49 GMT+01:00 Daniel Lezcano <daniel.lezcano@linaro.org>:
>> On 07/12/2017 17:33, Benjamin Gaignard wrote:
>>> 2017-12-07 16:27 GMT+01:00 Daniel Lezcano <daniel.lezcano@linaro.org>:
>>>> On 14/11/2017 09:52, Benjamin Gaignard wrote:
>>>>> The clock driving counters is at 90MHz so the maximum period
>>>>> for 16 bis counters is around 750 ms which is a short period
>>>>> for a clocksource.
>>>>
>>>> Isn't it 728us ?
>>>
>>> yes it is: 2^16 / 90.000.000 => 728us
>>
>> Ok, now I can do the connection with the previous patch.
>>
>> So, the real issue of all this is the 16bits clocksource is wrapping up
>> every 728us, hence the clockevent periodically expires every ~728us to
>> keep the timekeeping consistent. Unfortunately, the kernel has a too
>> high overhead for this as the system is consistently processing this
>> timer leading to a CPU time resource starvation.
>>
>> Is that correct ?
> 
> Yes that is correct

Oh man. That was unclear since the beginning, we are not talking about
inaccurate clocksource or whatever but just these 16bits timers can't
work on Linux.


-- 
 <http://www.linaro.org/> Linaro.org ? Open source software for ARM SoCs

Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog

  reply	other threads:[~2017-12-08  7:52 UTC|newest]

Thread overview: 58+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-11-14  8:52 [PATCH v8 0/6] stm32 clocksource driver rework Benjamin Gaignard
2017-11-14  8:52 ` Benjamin Gaignard
2017-11-14  8:52 ` Benjamin Gaignard
2017-11-14  8:52 ` [PATCH v8 1/6] clocksource: timer_of: rename timer_of_exit to timer_of_cleanup Benjamin Gaignard
2017-11-14  8:52   ` Benjamin Gaignard
2017-11-14  8:52   ` Benjamin Gaignard
2017-11-14 10:24   ` [tip:timers/urgent] clocksource/timer_of: Rename " tip-bot for Benjamin Gaignard
2017-11-14  8:52 ` [PATCH v8 2/6] clocksource: stm32: convert driver to timer_of Benjamin Gaignard
2017-11-14  8:52   ` Benjamin Gaignard
2017-11-14  8:52   ` Benjamin Gaignard
2017-11-14  8:52 ` [PATCH v8 3/6] clocksource: stm32: increase min delta value Benjamin Gaignard
2017-11-14  8:52   ` Benjamin Gaignard
2017-11-14  8:52   ` Benjamin Gaignard
2017-12-08  9:28   ` Daniel Lezcano
2017-12-08  9:28     ` Daniel Lezcano
2017-11-14  8:52 ` [PATCH v8 4/6] clocksource: stm32: only use 32 bits timers Benjamin Gaignard
2017-11-14  8:52   ` Benjamin Gaignard
2017-11-14  8:52   ` Benjamin Gaignard
2017-12-07 15:27   ` Daniel Lezcano
2017-12-07 15:27     ` Daniel Lezcano
2017-12-07 15:27     ` Daniel Lezcano
2017-12-07 16:33     ` Benjamin Gaignard
2017-12-07 16:33       ` Benjamin Gaignard
2017-12-07 16:49       ` Daniel Lezcano
2017-12-07 16:49         ` Daniel Lezcano
2017-12-07 20:36         ` Benjamin Gaignard
2017-12-07 20:36           ` Benjamin Gaignard
2017-12-08  7:52           ` Daniel Lezcano [this message]
2017-12-08  7:52             ` Daniel Lezcano
2017-12-08  7:52             ` Daniel Lezcano
2017-12-08  8:34   ` Daniel Lezcano
2017-12-08  8:34     ` Daniel Lezcano
2017-12-08  8:34     ` Daniel Lezcano
2017-12-08  9:25     ` Benjamin Gaignard
2017-12-08  9:25       ` Benjamin Gaignard
2017-12-08  9:25       ` Benjamin Gaignard
2017-12-08  9:29       ` Daniel Lezcano
2017-12-08  9:29         ` Daniel Lezcano
2017-12-08  9:29         ` Daniel Lezcano
2017-12-08  9:31         ` Benjamin Gaignard
2017-12-08  9:31           ` Benjamin Gaignard
2017-12-08  9:31           ` Benjamin Gaignard
2017-11-14  8:52 ` [PATCH v8 5/6] clocksource: stm32: add clocksource support Benjamin Gaignard
2017-11-14  8:52   ` Benjamin Gaignard
2017-11-14  8:52   ` Benjamin Gaignard
2017-11-14  8:52 ` [PATCH v8 6/6] arm: dts: stm32: remove useless clocksource nodes Benjamin Gaignard
2017-11-14  8:52   ` Benjamin Gaignard
2017-11-14  8:52   ` Benjamin Gaignard
2017-11-27 10:44 ` [PATCH v8 0/6] stm32 clocksource driver rework Benjamin Gaignard
2017-11-27 10:44   ` Benjamin Gaignard
2017-12-05 10:12 ` Alexandre Torgue
2017-12-05 10:12   ` Alexandre Torgue
2017-12-05 10:12   ` Alexandre Torgue
2017-12-05 10:15   ` Daniel Lezcano
2017-12-05 10:15     ` Daniel Lezcano
2017-12-05 10:16     ` Alexandre Torgue
2017-12-05 10:16       ` Alexandre Torgue
2017-12-05 10:16       ` Alexandre Torgue

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=4f9ed3dd-cf02-eed7-7fdd-38f8dc092eee@linaro.org \
    --to=daniel.lezcano@linaro.org \
    --cc=alexandre.torgue@st.com \
    --cc=arnd@arndb.de \
    --cc=benjamin.gaignard@linaro.org \
    --cc=devicetree@vger.kernel.org \
    --cc=julien.thierry@arm.com \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux@armlinux.org.uk \
    --cc=ludovic.barre@st.com \
    --cc=mark.rutland@arm.com \
    --cc=mcoquelin.stm32@gmail.com \
    --cc=robh+dt@kernel.org \
    --cc=sudeep.holla@arm.com \
    --cc=tglx@linutronix.de \
    /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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.