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From: Michael Schmitz <schmitzmic@gmail.com>
To: Russell King - ARM Linux <linux@armlinux.org.uk>
Cc: Finn Thain <fthain@telegraphics.com.au>,
	Christoph Hellwig <hch@infradead.org>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Arnd Bergmann <arnd@arndb.de>,
	Stephen N Chivers <schivers@csc.com.au>,
	Thomas Gleixner <tglx@linutronix.de>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	John Stultz <john.stultz@linaro.org>,
	linux-m68k@lists.linux-m68k.org, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [RFC PATCH 01/13] arm: Fix mutual exclusion in arch_gettimeoffset
Date: Thu, 15 Nov 2018 14:34:22 +1300
Message-ID: <b70ae231-19f2-ef7c-f7ca-0a6486d2cb6b@gmail.com> (raw)
In-Reply-To: <20181114075817.GQ30658@n2100.armlinux.org.uk>


On 14/11/18 8:58 PM, Russell King - ARM Linux wrote:
>
>> Are you saying that's not possible on arm, because the current timer rundown
>> counter can't be read while the timer is running?
>>
>> If I were to run a second timer at higher rate for clocksource, but keeping
>> the 10 ms timer as clock event (could easily do that by using timer D on
>> Atari Falcon) - how would that improve my timekeeping? Clock events still
>> only happen 10 ms apart ...
> Ah, I think you're talking about something else.
>
> You seem to be talking about what happens when time keeping interrupts
> happen.
That's what I understood your comment was about.
> I'm talking about the resolution of gettimeofday() and the other
> interfaces that are used (eg) for packet capture timestamping and
> the like - the _user_ visible effects of the timekeeping system.
>
> With the existing implementation, all these have better-than-jiffy
> resolution - in the case of RPC, that's 500ns, rather than 10ms
> which would be the case without gettimeoffset().  Removing
> gettimeoffset() as Finn has proposed without preserving that
> resolution is simply completely unacceptable.

I agree - but Finn had also offered to supply patches to arm that would 
have added a clocksource_read() function very much like for those m68k 
platforms that had used gettimeoffset(). I wondered what reason there 
was for these not to work on arm

I now realize you'd never seen that offer.

The proposal to drop architectures still relying on arch_gettimeoffset() 
had been raising enough of a response on linux-m68k to make me conclude 
that same proposal had been kicked on to other arch MLs affected as 
well. I'm a bit naive that way.

Now your criticism of arch_gettimeoffset() (missing timer rollover 
because the timer interrupt has been cleared by the interrupt handler) 
still stands. I just can't find the offset() functions shown in the 
5cfc8ee0bb51 patch. Any hints?

Cheers,

     Michael



  reply index

Thread overview: 53+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-12  4:12 [RFC PATCH 00/13] m68k: Drop arch_gettimeoffset and adopt clocksource API Finn Thain
2018-11-12  4:12 ` [RFC PATCH 08/13] m68k: atari: Convert to " Finn Thain
2018-11-12  4:12 ` [RFC PATCH 04/13] m68k: mac: Clean up unused timer definitions Finn Thain
2018-11-12  4:12 ` [RFC PATCH 10/13] m68k: hp300: Convert to clocksource API Finn Thain
2018-11-12  4:12 ` [RFC PATCH 11/13] m68k: mac: " Finn Thain
2018-11-12  4:12 ` [RFC PATCH 01/13] arm: Fix mutual exclusion in arch_gettimeoffset Finn Thain
2018-11-12  8:34   ` Christoph Hellwig
2018-11-13  3:39     ` Finn Thain
2018-11-13  9:20       ` Russell King - ARM Linux
2018-11-13 21:55         ` Finn Thain
2018-11-13 23:43           ` Russell King - ARM Linux
2018-11-14  1:35             ` Michael Schmitz
2018-11-14  7:58               ` Russell King - ARM Linux
2018-11-15  1:34                 ` Michael Schmitz [this message]
2018-11-14  3:17             ` Finn Thain
2018-11-14 14:16               ` Russell King - ARM Linux
2018-11-14 14:58                 ` Geert Uytterhoeven
2018-11-14 18:11                   ` Russell King - ARM Linux
2018-11-15  4:12                 ` Finn Thain
2018-11-16 17:47                   ` Russell King - ARM Linux
2018-11-16 22:49                     ` Finn Thain
2018-11-17  3:00                       ` Michael Schmitz
2018-11-14 12:05   ` Russell King - ARM Linux
2018-11-12  4:12 ` [RFC PATCH 02/13] m68k: " Finn Thain
2018-11-12  4:12 ` [RFC PATCH 07/13] m68k: amiga: Convert to clocksource API Finn Thain
2018-11-12  9:02   ` Geert Uytterhoeven
2018-11-12  9:21     ` Finn Thain
2018-11-12  4:12 ` [RFC PATCH 09/13] m68k: bvme6000: " Finn Thain
2018-11-12  4:12 ` [RFC PATCH 06/13] m68k: Drop ARCH_USES_GETTIMEOFFSET Finn Thain
2018-11-12  9:00   ` Geert Uytterhoeven
2018-11-12  9:06     ` Finn Thain
2018-11-13  2:29       ` Michael Schmitz
2018-11-13  3:14         ` Finn Thain
2018-11-13  4:50           ` Michael Schmitz
2018-11-13  6:15             ` Finn Thain
2018-11-13  8:24               ` Michael Schmitz
2018-11-13 22:11                 ` Finn Thain
2018-11-14  1:08                   ` Michael Schmitz
2018-11-14  2:58                     ` Michael Schmitz
2018-11-14 23:54                       ` Michael Schmitz
2018-11-15  4:37                         ` Finn Thain
2018-11-15  6:35                         ` Michael Schmitz
2018-11-16  0:04                           ` Finn Thain
2018-11-12  4:12 ` [RFC PATCH 13/13] m68k: mvme16x: Convert to clocksource API Finn Thain
2018-11-12 18:37   ` Thomas Gleixner
2018-11-13  0:11     ` Finn Thain
2018-11-13 22:04       ` Finn Thain
2018-11-13 22:10         ` [RFC PATCH 13/13] m68k: mvme16x: Convert to clocksource APIy Thomas Gleixner
2018-11-13 22:33           ` Finn Thain
2018-11-18 17:12             ` Thomas Gleixner
2018-11-12  4:12 ` [RFC PATCH 03/13] m68k: mac: Fix VIA timer counter accesses Finn Thain
2018-11-12  4:12 ` [RFC PATCH 12/13] m68k: mvme147: Convert to clocksource API Finn Thain
2018-11-12  4:12 ` [RFC PATCH 05/13] m68k: apollo, q40, sun3, sun3x: Remove arch_gettimeoffset implementations Finn Thain

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