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Date: Wed, 28 Oct 2015 13:15:37 -0700
From: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
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To: Alex Smith <alex@alex-smith.me.uk>
CC: David Daney <ddaney.cavm@gmail.com>, Ralf Baechle <ralf@linux-mips.org>,
        Markos Chandras <markos.chandras@imgtec.com>,
        linux-mips <linux-mips@linux-mips.org>,
        Alex Smith <alex.smith@imgtec.com>, <linux-kernel@vger.kernel.org>
Subject: Re: [v3, 3/3] MIPS: VDSO: Add implementations of gettimeofday() and
 clock_gettime()
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On 10/28/2015 12:55 PM, Alex Smith wrote:
> On 28 October 2015 at 19:28, Leonid Yegoshin <Leonid.Yegoshin@imgtec.com> wrote:
>> . 
> Clocksources are not per-CPU. If the CP0 counter is the current
> clocksource, then both the kernel and VDSO implementations of
> gettimeofday will read out the CP0 counter from whatever CPU they run
> on.

OK, it was an invalid example. Let's be specific - in case of different 
clock frequency in different CPUs it easy to adjust it in kernel via 
clocksource->read()/etc but it is impossible to adjust that in VDSO 
implementation.

And that can't be fixed easily without some-kind of "per-thread" data 
page for correct multipliers.

There are many problems with assumption that in all kind of MIPS cores 
R4K CP0_COUNT registers are in sync in different CPUs. Even current 
kernel has problems here but I think it is not excuse to mount more on it.

- Leonid.