linux-kernel - Re: CONFIG_NO_HZ: missed ticks, stall (keyb IRQ required) [2.6.18-rc4-mm1]

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Message-ID: <20061107082434.GA13585@elte.hu>
Date:	Tue, 7 Nov 2006 09:24:35 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Andreas Mohr <andi@...x01.fht-esslingen.de>
Cc:	Len Brown <lenb@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: CONFIG_NO_HZ: missed ticks, stall (keyb IRQ required) [2.6.18-rc4-mm1]

* Andreas Mohr <andi@...x01.fht-esslingen.de> wrote:

> The results are (waited for values to settle down each time):
> 
> -dyntick4, C1, CONFIG_NO_HZ:
>      83.9W KDE idle, 95.2W bash while 1
> -dyntick4, C2 (C1-only hack disabled, kernel rebuilt), CONFIG_NO_HZ off:
>      84.4W KDE idle, 95.4W bash while 1
> -dyntick4, acpi=off (i.e. APM active), -dynticks:
>      85.5W KDE idle, 95.5W bash while 1
> 
> Bet you didn't see this coming...

interesting that there's any savings from dynticks in this workload. 
When the CPU is busy then dynticks generates the usual HZ scheduler 
tick.

could you try the same measurement with a completely idle system too? 
That is where dynticks has its true effects: longer idle intervals. (but 
even on an idle system dynticks might not make a difference unless the 
hardware can utilize the much larger and more predictable idle times 
that dynticks offers.)

	Ingo
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