From: Frans Pop <elendil@planet.nl>
To: Thomas Gleixner <tglx@linutronix.de>
Subject: Re: Bootup time regression from 2.6.27 to 2.6.28-rc3+
Date: Fri, 14 Nov 2008 02:45:38 +0100
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Cc: Arjan van de Ven <arjan@infradead.org>,
       Lukas Hejtmanek <xhejtman@ics.muni.cz>,
       "Rafael J. Wysocki" <rjw@sisk.pl>,
       Marcin Slusarz <marcin.slusarz@gmail.com>, linux-kernel@vger.kernel.org,
       torvalds@linux-foundation.org, corsac@debian.org
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Hi Thomas/Arjan,

On Sunday 09 November 2008, Thomas Gleixner wrote:
> I worked all week after returning from travelling to get down to the
> root cause of this. We had several issues:
>
> 1) peek_ahead confused the hell out of the nohz code when it expired
> timers when the timer interrupt was already pending
>
> 2) the changes I did to prevent the stale jiffies in the nohz case
> turned out to be incomplete and wrong versus the broadcast of timers
> in deeper C-States
>
> 3) the consolidation of the nohz idle checks called the nohz jiffies
> update code before calling __irq_enter() which caused useless wakeups
> of ksoftirqd
>
> 4) A long standing - but until now papered over and therefor unnoticed
> - problem of spurious wakeups from deep c-states:
>
>   If one core gets an interrupt the other core(s) wake up as
>   well. The stale jiffies fix and the peek_ahead changes made this
>   more visible and is a major part of the reported nohz (more wakeups,
>   more power consumption) regression.
>
>   This was there forever, but nobody noticed as it was not accounted
>   for.
>
> Find below the lineup of the timers-fixes-for-linus branch of the tip
> tree (the same as Arjan posted minus the irq fixes)

Could either of you maybe give a status update on this patch set and the 
remaining issues with it that were reported (especially the high C0 
reported by powertop)?

TIA,
FJP
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