linux-kernel - Re: [PATCH] Allow CLOCK_TICK

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Message-ID: <20120719092239.GB28942@arm.com>
Date:	Thu, 19 Jul 2012 10:22:39 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	John Stultz <john.stultz@...aro.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH] Allow CLOCK_TICK_RATE to be undefined

On Thu, Jul 19, 2012 at 12:11:03AM +0100, John Stultz wrote:
> On 07/18/2012 03:51 PM, Andrew Morton wrote:
> > On Tue, 17 Jul 2012 17:41:40 +0100
> > Catalin Marinas <catalin.marinas@....com> wrote:
> >
> >> This patch allows an architecture to not define CLOCK_TICK_RATE, in
> >> which case ACTHZ defaults to (HZ << 8).
> > No reason was given for this change.
> >
> > So those people who are wondering "why don't you just define
> > CLOCK_TICK_RATE" are made all sad.
> 
> I just queued this patch with a revised commit message:
> 
>      jiffies: Allow CLOCK_TICK_RATE to be undefined
> 
>      CLOCK_TICK_RATE is a legacy constant that defines the timer
>      device's granularity. On hardware with particularly coarse
>      granularity, this constant is used to reduce accumulated
>      time error when using jiffies as a clocksource, by calculating
>      the hardware's actual tick length rather then just assuming
>      it is 1sec/HZ.
> 
>      However, for the most part this is unnecessary, as most modern
>      systems don't use jiffies for their clocksource, and their
>      tick device is sufficiently fine grained to avoid major error.
> 
>      Thus, this patch allows an architecture to not define
>      CLOCK_TICK_RATE, in which case ACTHZ defaults to (HZ << 8).
> 
> 
> Let me know if you'd like to see further improvements.

Looks good. Thanks for picking this up.

-- 
Catalin
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