linux-kernel - Re: [PATCH 1/2] jiffies: Allow CLOCK_TICK

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Message-ID: <20120726125620.GD24672@gmail.com>
Date:	Thu, 26 Jul 2012 14:56:20 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	John Stultz <john.stultz@...aro.org>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Richard Cochran <richardcochran@...il.com>,
	Prarit Bhargava <prarit@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1/2] jiffies: Allow CLOCK_TICK_RATE to be undefined


* John Stultz <john.stultz@...aro.org> wrote:

> On 07/19/2012 02:37 AM, Ingo Molnar wrote:
> >* John Stultz <john.stultz@...aro.org> wrote:
> >
> >>From: Catalin Marinas <catalin.marinas@....com>
> ...
> >>diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h
> >>index 265e2c3..a2134be 100644
> >>--- a/include/linux/jiffies.h
> >>+++ b/include/linux/jiffies.h
> >>@@ -39,9 +39,6 @@
> >>  # error Invalid value of HZ.
> >>  #endif
> >>-/* LATCH is used in the interval timer and ftape setup. */
> >>-#define LATCH  ((CLOCK_TICK_RATE + HZ/2) / HZ)	/* For divider */
> >>-
> >>  /* Suppose we want to divide two numbers NOM and DEN: NOM/DEN, then we can
> >>   * improve accuracy by shifting LSH bits, hence calculating:
> >>   *     (NOM << LSH) / DEN
> >>@@ -54,8 +51,15 @@
> >>  #define SH_DIV(NOM,DEN,LSH) (   (((NOM) / (DEN)) << (LSH))              \
> >>                               + ((((NOM) % (DEN)) << (LSH)) + (DEN) / 2) / (DEN))
> >>+#ifdef CLOCK_TICK_RATE
> >>+/* LATCH is used in the interval timer and ftape setup. */
> >>+#define LATCH ((CLOCK_TICK_RATE + HZ/2) / HZ)	/* For divider */
> >>+
> >>  /* HZ is the requested value. ACTHZ is actual HZ ("<< 8" is for accuracy) */
> >>  #define ACTHZ (SH_DIV (CLOCK_TICK_RATE, LATCH, 8))
> >>+#else
> >>+#define ACTHZ (HZ << 8)
> >>+#endif
> >The ACTHZ naming ugliness slipped past me. 'ACT' can mean so
> >many things - please improve it to something more obvious, like
> >'REAL_HZ' or 'KERNEL_HZ'.
> 
> ACTHZ has been around for a while. ~2002 I think?

Time flies!

> Is it ok if I do the rename in a following patch?

Sure.

> >Also, we tend to write such #if/#else/#endif patterns as:
> >
> >#if FOO
> ># define BAR
> >#else
> ># define BAZ
> >#endif
> I'll fix this.

Thanks!

	Ingo
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