linux-kernel - Re: [v3, 3/3] MIPS: VDSO: Add implementations of gettimeofday() and clock

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Message-ID: <563121D5.4030601@imgtec.com>
Date:	Wed, 28 Oct 2015 12:28:21 -0700
From:	Leonid Yegoshin <Leonid.Yegoshin@...tec.com>
To:	Alex Smith <alex@...x-smith.me.uk>
CC:	David Daney <ddaney.cavm@...il.com>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Markos Chandras <markos.chandras@...tec.com>,
	linux-mips <linux-mips@...ux-mips.org>,
	Alex Smith <alex.smith@...tec.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [v3, 3/3] MIPS: VDSO: Add implementations of gettimeofday() and
 clock_gettime()

On 10/28/2015 12:04 PM, Alex Smith wrote:
> On 28 October 2015 at 18:57, Leonid Yegoshin <Leonid.Yegoshin@...tec.com> wrote:
>>
> As I've explained the VDSO will only use the CP0 counter in the same
> situations that the kernel would when it is the active clocksource.
> Any issue that makes the counter unreliable affects the kernel as well
> and is unrelated to the VDSO, so a fix does not belong in this patch.

What would you do if some SoC with different type of cores will define 
CPU1 etc CP0_COUNT as a DIFFERENT clocksource from CPU0 (because of 
frequency etc)? Timekeeping can select CPU0 clocksource but code still 
uses a local CPU1 CP0_COUNT for gettimeofday().

And this kind of solution is the first in line to have an accurate 
timing in systems without GIC and with different clock frequencies.

- Leonid

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