linux-kernel - Re: [RFC PATCH 06/13] m68k: Drop ARCH_USES

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Message-ID: <b824e485-796c-cbb6-9e50-504b03accd5d@gmail.com>
Date:   Tue, 13 Nov 2018 17:50:37 +1300
From:   Michael Schmitz <schmitzmic@...il.com>
To:     Finn Thain <fthain@...egraphics.com.au>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Arnd Bergmann <arnd@...db.de>,
        Stephen N Chivers <schivers@....com.au>,
        Thomas Gleixner <tglx@...utronix.de>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        John Stultz <john.stultz@...aro.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Philip Blundell <philb@....org>,
        Joshua Thompson <funaho@...ai.org>
Subject: Re: [RFC PATCH 06/13] m68k: Drop ARCH_USES_GETTIMEOFFSET

Hi Finn,

Am 13.11.2018 um 16:14 schrieb Finn Thain:
> On Tue, 13 Nov 2018, Michael Schmitz wrote:
>
>> Hi Finn,
>>
>> Am 12.11.2018 um 22:06 schrieb Finn Thain:
>>> On Mon, 12 Nov 2018, Geert Uytterhoeven wrote:
>>>
>>>> Hi Finn,
>>>>
>>>> Thanks for your patch!
>>>>
>>>> On Mon, Nov 12, 2018 at 5:46 AM Finn Thain <fthain@...egraphics.com.au>
>>>> wrote:
>>>>> The functions that implement arch_gettimeoffset are re-used by
>>>>> new clocksource drivers in subsequent patches.
>>>>
>>>> Disabling this first affects functionality during bisection, right?
>>>>
>>>
>>> It means that all platforms have to use the 'jiffies' clocksource.
>>
>> So all that happens is timer granularity drops to 10ms, then gets restored by
>> the later patches?
>>
>
> Yes, that was the plan, but I can't confirm that it worked out as I don't
> have any physical 68k hardware in front of me right now. If you can
> confirm this on your Atari Falcon, that would be great.

Will do.

> (It appears that a QEMU-emulated Mac does not benefit from having a
> clocksource that's more accurate than the 'jiffies' clocksource, in spite
> of "clocksource: Switched to clocksource via1".)

With the current code, kernel log timestamps have 10 ms resolution on 
Atari. Time resolution of times reported by initcall_debug is roughly 40 
us. I'd expect that changes with falling back to jiffies only. Might be 
worth a try on QEMU Mac.

Cheers,

	Michael

> The latest patches can be found at
> https://github.com/fthain/linux/commits/mac68k-queue/
>