linux-kernel - Re: HPET causes tasks to freeze (still in 2.6.36-rc6)

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Message-ID: <20101004175506.3e6b8c2b@tux.DEF.witbe.net>
Date:	Mon, 4 Oct 2010 17:55:06 +0200
From:	Paul Rolland (ポール・ロラン) 
	<rol@...be.net>
To:	Jiri Slaby <jslaby@...e.cz>
Cc:	LKML <linux-kernel@...r.kernel.org>, clemens@...isch.de,
	venki@...gle.com, Thomas Gleixner <tglx@...utronix.de>,
	the arch/x86 maintainers <x86@...nel.org>, rol@...be.net
Subject: Re: HPET causes tasks to freeze (still in 2.6.36-rc6)

Hello,

On Mon, 04 Oct 2010 17:36:17 +0200
Jiri Slaby <jslaby@...e.cz> wrote:

> HPET as a clocksource has still issues in the latest kernels (confirmed
> in 2.6.36-rc6) at least on x86_64. Unless clocksource=jiffies,
> clocksource=tsc or nolapic_timer is used, the system is unusable. Tasks
> are not woken unless mouse is moved, key is pressed (or other hard irq
> triggered). 2.6.32 seems to be the last working.
> 
> The bug was originally reported in the bugzilla here:
> https://bugzilla.novell.com/show_bug.cgi?id=579932
> 
> To quote:
> "My clock is seriously lagging behind. After having used hpet for 10.5
> hours now, the clock is 5.5 hours too late!"
> 
> dmesg is attached. Any ideas what's still wrong with HPET?

I've been experiencing that also with some Supermicro servers...

and last week, I switched to 2.6.35.5, which is now no more exhibiting this
weird behavior, but it may be because the machine has elected tsc as its
clocksource.

I must also say that kernels before 2.6.35.5 (namely 2.6.28.9) were showing
this strange behavior whatever clocksource I was using, so it was not
specifically HPET-related, but the "Tasks are not woken unless mouse is moved,
key is pressed (or other hard irq triggered)" part was exactly what i was 
experiencing.

Paul
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