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From: Marc Gonzalez <marc_gonzalez@sigmadesigns.com>
To: Nicolas Pitre <nicolas.pitre@linaro.org>
Cc: Russell King - ARM Linux <linux@armlinux.org.uk>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Alan Cox <gnomes@lxorguk.ukuu.org.uk>,
	LKML <linux-kernel@vger.kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ingo Molnar <mingo@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	"Peter Zijlstra" <peterz@infradead.org>,
	John Stultz <john.stultz@linaro.org>,
	Douglas Anderson <dianders@chromium.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	Jonathan Austin <jonathan.austin@arm.com>,
	Arnd Bergmann <arnd@arndb.de>, Kevin Hilman <khilman@kernel.org>,
	Michael Turquette <mturquette@baylibre.com>,
	"Stephen Boyd" <sboyd@codeaurora.org>,
	Boris Brezillon <boris.brezillon@free-electrons.com>,
	Thibaud Cornic <thibaud_cornic@sigmadesigns.com>,
	Mason <slash.tmp@free.fr>
Subject: Re: [RFC] Improving udelay/ndelay on platforms where that is possible
Date: Thu, 16 Nov 2017 17:51:05 +0100	[thread overview]
Message-ID: <870aeb80-bbc5-52ed-cca2-3e762e27bfe2@sigmadesigns.com> (raw)
In-Reply-To: <nycvar.YSQ.7.76.1711161140030.20817@knanqh.ubzr>

On 16/11/2017 17:47, Nicolas Pitre wrote:

> Look at cpufreq_callback() in arch/arm/kernel/smp.c.

Are you pointing at the scaling of loops_per_jiffy done in that function?

As I wrote earlier:

If I'm reading arch/arm/kernel/smp.c correctly, loops_per_jiffy is scaled
when the frequency changes.

But arch/arm/lib/delay-loop.S starts by loading the current value of
loops_per_jiffy, computes the number of times to loop, and then loops.
If the frequency increases when the core is in __loop_delay, the
delay will be much shorter than requested.

  reply	other threads:[~2017-11-16 16:51 UTC|newest]

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-10-31 16:15 [RFC] Improving udelay/ndelay on platforms where that is possible Marc Gonzalez
2017-10-31 16:44 ` Linus Torvalds
2017-10-31 16:56   ` Russell King - ARM Linux
2017-10-31 17:45     ` Linus Torvalds
2017-10-31 17:58       ` Linus Torvalds
2017-11-01  0:23       ` Doug Anderson
2017-11-01  9:26         ` Russell King - ARM Linux
2017-11-01 15:53           ` Doug Anderson
2017-12-07 12:31             ` Pavel Machek
2017-11-01 19:28           ` Marc Gonzalez
2017-11-01 20:30             ` Russell King - ARM Linux
2017-10-31 16:46 ` Russell King - ARM Linux
2017-11-01 17:53 ` Alan Cox
2017-11-01 19:03   ` Marc Gonzalez
2017-11-01 19:09     ` Linus Torvalds
2017-11-01 19:17       ` Linus Torvalds
2017-11-01 19:38       ` Marc Gonzalez
2017-11-15 12:51         ` Marc Gonzalez
2017-11-15 13:13           ` Russell King - ARM Linux
2017-11-16 15:26             ` Marc Gonzalez
2017-11-16 15:36               ` Russell King - ARM Linux
2017-11-16 15:47                 ` Marc Gonzalez
2017-11-16 16:08                   ` Nicolas Pitre
2017-11-16 16:26                     ` Marc Gonzalez
2017-11-16 16:32                       ` Russell King - ARM Linux
2017-11-16 16:42                         ` Marc Gonzalez
2017-11-16 17:05                           ` Russell King - ARM Linux
2017-11-16 21:05                             ` Marc Gonzalez
2017-11-16 22:15                               ` Doug Anderson
2017-11-16 23:22                                 ` Russell King - ARM Linux
2017-11-20 17:38                                   ` Doug Anderson
2017-11-20 18:31                                     ` Russell King - ARM Linux
2017-11-16 16:47                       ` Nicolas Pitre
2017-11-16 16:51                         ` Marc Gonzalez [this message]
2017-11-16 17:00                           ` Nicolas Pitre
2017-12-07 12:43             ` Pavel Machek
2017-11-15 18:45           ` Doug Anderson
2017-11-01 19:36     ` Alan Cox
2017-11-01 19:39     ` Thomas Gleixner
2017-11-01 19:48     ` Baruch Siach
2017-11-02 16:12       ` Boris Brezillon

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