linux-kernel - Re: [patch-mm 00/28] High resolution timer updates and x86_64 support

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Date:	Thu, 28 Jun 2007 02:42:33 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Andi Kleen <ak@...e.de>, Ingo Molnar <mingo@...e.hu>,
	Arjan van de Ven <arjan@...radead.org>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	John Stultz <johnstul@...ibm.com>,
	Chris Wright <chrisw@...s-sol.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [patch-mm 00/28] High resolution timer updates and x86_64
 support - V3

On Sat, 23 Jun 2007 13:32:25 -0000 Thomas Gleixner <tglx@...utronix.de> wrote:

> The following patch series contains:
> 
> - dyntick bugfixes for -mm (caused by the cpuidle changes in ACPI)
> 
> - updates and improvements to high resolution timer / dynticks 
> 
> - high resolution timer / dynticks support for x86_64

Blam.  http://userweb.kernel.org/~akpm/hpet-crash.jpg

time_init() is called before slab is set up.  We cannot do memory
allocations inside time_init().

> The patch set has been tested in the -hrt and -rt trees for quite a while
> and the initial problems have been sorted out. Thanks to the folks from the
> PowerTop project for testing and feedback.

hrm.  Looks like none of your testers have HPET_ID_LEGSUP hardware.  This:

--- a/arch/i386/kernel/hpet.c~a
+++ a/arch/i386/kernel/hpet.c
@@ -376,7 +376,7 @@ int __init hpet_enable(void)
 
 	clocksource_register(&clocksource_hpet);
 
-	if (id & HPET_ID_LEGSUP) {
+	if (0 && (id & HPET_ID_LEGSUP)) {
 		hpet_enable_int();
 		hpet_reserve_platform_timers(id);
 		/*
_

gets it working.  It basically nobbles the hpet and the kernel chose the
TSC clocksource instead.


btw, if you want to know why I go on and on about crappy commenting, try to
work out from the kernel source code what HPET_ID_LEGSUP is, and why it
gets special treatment.  It is not possible.  This is not maintainable
code.

-
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