linux-kernel - Re: 2.6.24-rc6-git12: Reported regressions from 2.6.23

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Date:	Sun, 6 Jan 2008 23:36:17 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Mark Lord <lkml@....ca>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Adrian Bunk <bunk@...nel.org>
Subject: Re: 2.6.24-rc6-git12: Reported regressions from 2.6.23

On Sunday, 6 of January 2008, Arjan van de Ven wrote:
> On Sun, 6 Jan 2008 10:55:01 +0100
> Ingo Molnar <mingo@...e.hu> wrote:
> 
> > 
> > * Mark Lord <lkml@....ca> wrote:
> > 
> > > Rafael J. Wysocki wrote:
> > >> This message contains a list of some regressions from 2.6.23
> > >> reported since 2.6.24-rc1 was released, for which there are no
> > >> fixes in the mainline I know of.  If any of them have been fixed
> > >> already, please let me know.
> > > ..
> > >> Subject		: 20000+ wake-ups/second in 2.6.24
> > >> Submitter	: Mark Lord <lkml@....ca>
> > >> Date		: 2007-12-02 04:23
> > >> References	: http://lkml.org/lkml/2007/12/1/141
> > >> 		  http://bugzilla.kernel.org/show_bug.cgi?id=9489
> > >> Handled-By	: Arjan van de Ven <arjan@...radead.org>
> > >>
> > >
> > > I wonder if it's just a babbling IRQ on resume, before the driver
> > > has run it's resume code or something ?
> > 
> > i've read the discussions, and i cannot see it analyzed anywhere
> > _what_ causes the wakeups. And how are these wakeups counted? Is this
> > based on powertop output:
> > 
> >  Wakeups-from-idle per second : 20.4     interval: 1.8s
> > 
> > ? Somewhere i saw it mentioned that "the CPU throws out of C mode".
> > What does that mean - does it mean we try to idle again and again,
> > but we immediately return from C mode - while this all looks like
> > "idle" time to the scheduler (so 'top' will show lots of idle time),
> > but the ACPI wakeup counters are going up like mad? What
> > is /proc/interrupts doing when this happens - is any of the irq
> > sources going upwards?
> > 
> 
> what seems to happen (and this is based on seeing this on my own devel laptop, as well
> as several other reports; Mark is by far not the only one) is something hardware
> related, it's been seen on lots of different kernel versions.
> 
> It seems to mostly (but not 100%) happen with TI cardbus bridges, where for some reason,
> once the yenta driver is loaded (unloading it later makes no difference), once in a while
> we get into a mode where the CPU always immediately goes out of the C-state again.
> On a hardware level, there are only a few things that cause a CPU to exit a C-state,
> and one of them is a pending interrupt of some kind, which is the most likely thing going on here;
> some device or apic being stuck with interrupt high, but somehow the CPU isn't actually
> seeing the interrupt itself (or has it blocked!)
> 
> To call this a 2.6.24 regression is a mistake (as I've said before), it's not new to .24
> by any means.

Thanks for the explanation, I'm removing this from the regressions list, then.

Greetings,
Rafael
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