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From: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
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()
Date: Wed, 28 Oct 2015 13:15:37 -0700	[thread overview]
Message-ID: <56312CE9.3090301@imgtec.com> (raw)
In-Reply-To: <CAOFt0_DKfouP0r68M8S-CQF=Fk0C7sPpV2WNm=u-wH3_1q=Pzw@mail.gmail.com>

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.

WARNING: multiple messages have this Message-ID (diff)
From: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
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()
Date: Wed, 28 Oct 2015 13:15:37 -0700	[thread overview]
Message-ID: <56312CE9.3090301@imgtec.com> (raw)
Message-ID: <20151028201537.6f3sWliIaEMGsYh-Xnn-4aiGYNkZzAfm5YsMfnG_9D4@z> (raw)
In-Reply-To: <CAOFt0_DKfouP0r68M8S-CQF=Fk0C7sPpV2WNm=u-wH3_1q=Pzw@mail.gmail.com>

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.

  reply	other threads:[~2015-10-28 20:15 UTC|newest]

Thread overview: 58+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-09-28 10:03 [PATCH 0/3] MIPS VDSO support Markos Chandras
2015-09-28 10:03 ` Markos Chandras
2015-09-28 10:10 ` [PATCH 1/3] MIPS: Initial implementation of a VDSO Markos Chandras
2015-09-28 10:10   ` Markos Chandras
2015-09-28 10:54   ` Alex Smith
2015-09-28 13:07     ` Matthew Fortune
2015-11-20 18:15       ` Maciej W. Rozycki
2015-10-09  8:05   ` [PATCH v2 " Markos Chandras
2015-10-09  8:05     ` Markos Chandras
2015-10-21  8:54     ` [PATCH v3 " Markos Chandras
2015-10-21  8:54       ` Markos Chandras
2015-09-28 10:11 ` [PATCH 2/3] irqchip: irq-mips-gic: Provide function to map GIC user section Markos Chandras
2015-09-28 10:11   ` Markos Chandras
2015-09-28 10:55   ` Marc Zyngier
2015-09-28 14:16     ` Qais Yousef
2015-09-28 14:16       ` Qais Yousef
2015-09-28 15:03       ` Marc Zyngier
2015-10-05  8:22     ` Markos Chandras
2015-10-05  8:22       ` Markos Chandras
2015-10-12  9:40   ` [PATCH v2 " Markos Chandras
2015-10-12  9:40     ` Markos Chandras
2015-10-12  9:51     ` Marc Zyngier
2015-10-12 10:16       ` Thomas Gleixner
2015-10-15  9:37         ` Qais Yousef
2015-10-15  9:37           ` Qais Yousef
2015-10-15 10:18           ` Thomas Gleixner
2015-09-28 10:12 ` [PATCH 3/3] MIPS: VDSO: Add implementations of gettimeofday() and clock_gettime() Markos Chandras
2015-09-28 10:12   ` Markos Chandras
2015-09-28 13:15   ` kbuild test robot
2015-09-28 13:15     ` kbuild test robot
2015-10-12 10:24   ` [PATCH v2 " Markos Chandras
2015-10-12 10:24     ` Markos Chandras
2015-10-21  8:57     ` [PATCH v3 " Markos Chandras
2015-10-21  8:57       ` Markos Chandras
2015-10-23  1:41       ` [v3, " Leonid Yegoshin
2015-10-23  1:41         ` Leonid Yegoshin
2015-10-27 14:47         ` Ralf Baechle
2015-10-27 20:46           ` Leonid Yegoshin
2015-10-27 20:46             ` Leonid Yegoshin
2015-10-27 21:02             ` David Daney
2015-10-27 21:15               ` Leonid Yegoshin
2015-10-27 21:15                 ` Leonid Yegoshin
2015-10-27 21:44                 ` David Daney
2015-10-27 21:49                   ` Leonid Yegoshin
2015-10-27 21:49                     ` Leonid Yegoshin
2015-10-28 10:20                     ` Alex Smith
2015-10-28 18:21                       ` Leonid Yegoshin
2015-10-28 18:21                         ` Leonid Yegoshin
2015-10-28 18:30                         ` Alex Smith
2015-10-28 18:57                           ` Leonid Yegoshin
2015-10-28 18:57                             ` Leonid Yegoshin
2015-10-28 19:04                             ` Alex Smith
2015-10-28 19:28                               ` Leonid Yegoshin
2015-10-28 19:28                                 ` Leonid Yegoshin
2015-10-28 19:55                                 ` Alex Smith
2015-10-28 20:15                                   ` Leonid Yegoshin [this message]
2015-10-28 20:15                                     ` Leonid Yegoshin
2016-01-25 22:36       ` [PATCH v3 " Hauke Mehrtens

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