From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: Mason <mpeg.blue@free.fr>
Cc: Stefan Agner <stefan@agner.ch>,
Mark Rutland <mark.rutland@arm.com>,
Linux PM <linux-pm@vger.kernel.org>,
Stephen Boyd <sboyd@codeaurora.org>,
Rob Herring <rob.herring@calxeda.com>,
cpufreq <cpufreq@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: Delays, clocks, timers, hrtimers, etc
Date: Sat, 7 Feb 2015 09:51:35 +0000 [thread overview]
Message-ID: <20150207095135.GB8656@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <54D576B1.4000001@free.fr>
On Fri, Feb 06, 2015 at 06:21:37PM -0800, Mason wrote:
> Also, reading arch/arm/kernel/smp_twd.c, I see that frequency changes
> due to cpufreq are properly accounted for. (Although I imagine they do
> introduce a small error in time-keeping because moving from freq_A to
> freq_B is not instantaneous, so the exact time elapsed in-between is
> impossible to determine.)
TWD is not used for time keeping as such. As I explained in one of my
previous emails, local timers are used to signal events.
The active clocksource is used to determine the passing of time-of-day,
and sched_clock is used to account for process time by the scheduler.
An early/late/missed local timer interrupt has no impact on time keeping.
--
FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up
according to speedtest.net.
WARNING: multiple messages have this Message-ID (diff)
From: linux@arm.linux.org.uk (Russell King - ARM Linux)
To: linux-arm-kernel@lists.infradead.org
Subject: Delays, clocks, timers, hrtimers, etc
Date: Sat, 7 Feb 2015 09:51:35 +0000 [thread overview]
Message-ID: <20150207095135.GB8656@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <54D576B1.4000001@free.fr>
On Fri, Feb 06, 2015 at 06:21:37PM -0800, Mason wrote:
> Also, reading arch/arm/kernel/smp_twd.c, I see that frequency changes
> due to cpufreq are properly accounted for. (Although I imagine they do
> introduce a small error in time-keeping because moving from freq_A to
> freq_B is not instantaneous, so the exact time elapsed in-between is
> impossible to determine.)
TWD is not used for time keeping as such. As I explained in one of my
previous emails, local timers are used to signal events.
The active clocksource is used to determine the passing of time-of-day,
and sched_clock is used to account for process time by the scheduler.
An early/late/missed local timer interrupt has no impact on time keeping.
--
FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up
according to speedtest.net.
next prev parent reply other threads:[~2015-02-07 9:51 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-01-28 13:16 Delays, clocks, timers, hrtimers, etc Mason
2015-01-28 13:16 ` Mason
2015-01-29 13:57 ` Mason
2015-01-29 13:57 ` Mason
2015-02-03 12:09 ` Russell King - ARM Linux
2015-02-03 12:09 ` Russell King - ARM Linux
2015-02-06 18:37 ` Mason
2015-02-06 18:37 ` Mason
2015-02-06 19:14 ` Russell King - ARM Linux
2015-02-06 19:14 ` Russell King - ARM Linux
2015-02-06 21:03 ` Mason
2015-02-06 21:03 ` Mason
2015-02-07 10:42 ` Russell King - ARM Linux
2015-02-07 10:42 ` Russell King - ARM Linux
2015-02-09 7:45 ` Michal Simek
2015-02-09 7:45 ` Michal Simek
2015-02-09 16:10 ` Sören Brinkmann
2015-02-09 16:10 ` Sören Brinkmann
2015-02-09 23:27 ` Mason
2015-02-09 23:27 ` Mason
2015-02-06 20:25 ` Stefan Agner
2015-02-06 20:25 ` Stefan Agner
2015-02-06 21:17 ` Mason
2015-02-06 21:17 ` Mason
2015-02-06 21:31 ` Stefan Agner
2015-02-06 21:31 ` Stefan Agner
2015-02-07 2:21 ` Mason
2015-02-07 2:21 ` Mason
2015-02-07 9:51 ` Russell King - ARM Linux [this message]
2015-02-07 9:51 ` Russell King - ARM Linux
2015-02-09 19:01 ` Stephen Boyd
2015-02-09 19:01 ` Stephen Boyd
2015-02-09 22:31 ` Mason
2015-02-09 22:31 ` Mason
2015-02-09 23:17 ` Stephen Boyd
2015-02-09 23:17 ` Stephen Boyd
2015-02-09 23:50 ` Mason
2015-02-09 23:50 ` Mason
2015-02-11 17:43 ` Mason
2015-02-11 17:43 ` Mason
2015-02-11 18:45 ` Stephen Boyd
2015-02-11 18:45 ` Stephen Boyd
2015-02-11 21:58 ` Mason
2015-02-11 21:58 ` Mason
2015-02-11 23:26 ` Stephen Boyd
2015-02-11 23:26 ` Stephen Boyd
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