linux-kernel - Re: HPET : Legacy Routing Replacement Enable

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Message-ID: <20061027070319.GA24559@suse.cz>
Date:	Fri, 27 Oct 2006 09:03:19 +0200
From:	Vojtech Pavlik <vojtech@...e.cz>
To:	Mika Penttilä <mika.penttila@...umbus.fi>
Cc:	Andi Kleen <ak@....de>, Om Narasimhan <om.turyx@...il.com>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	linux-kernel@...r.kernel.org, randy.dunlap@...cle.com,
	clemens@...isch.de, bob.picco@...com
Subject: Re: HPET : Legacy Routing Replacement Enable - 3rd try.

On Fri, Oct 27, 2006 at 09:29:44AM +0300, Mika Penttilä wrote:

> >JFYI: The new per-cpu timekeeping code doesn't need the HPET legacy bit,
> >thus not replacing IRQ0 (PIT) and IRQ13 (RTC). It still can do that, but
> >will work just as well without it.

> There seems to be lot of confusion here. Current code isn't using hpet 
> as tick source if legacy is not supported. This patch adds 
> hpet_lrr_force but it's not clear how it interacts with hpet_use_timer - 
> in some places it is hpet_use_timer and some (hpet_use_timer && 
> hpet_lrr_force).

Sorry about my share of confusion introduced: Jiri Bohac
(jbohac@...e.cz) is currently working on a new timekeeping code for
x86-64 that takes a significantly different approach that allows for
precise and fast gettimeofday even on CPUs with unsynchronized TSCs.

This rewrite depends even less on hpet_use_timer than the current code.
The current code can cope with hpet_use_timer == 0, but that mode of
operation is far from optimal.

> The timer is routed to ioapic pin 2 which is irq0 with source override. 
> With this patch with hpet_lrr_force=1 timer irq is set to 2 for x86_64 
> and 0 for i386, that can't be right?
 
It doesn't seem right to me, unless someone at Sun really misread the
specification when designing the mainboard.

-- 
Vojtech Pavlik
Director SuSE Labs
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