linux-kernel - nmi_watchdog killing tickless feature

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Message-Id: <20071225043654.M32161@visp.net.lb>
Date:	Tue, 25 Dec 2007 06:36:54 +0200
From:	"Denys Fedoryshchenko" <denys@...p.net.lb>
To:	linux-kernel@...r.kernel.org
Subject: nmi_watchdog killing tickless feature

Hi

Please CC me on reply, i am not subscribed to list.

I did small test, and notice that if nmi_watchdog is enabled
mpstat 1

06:11:00     CPU   %user   %nice    %sys %iowait    %irq   %soft  %steal  
%idle    intr/s
06:11:01     all    0.00    0.00    0.00    0.00    0.00    0.00    0.00 
100.00    993.07
06:11:02     all    0.00    0.00    0.00    0.00    0.00    0.00    0.00 
100.00   1007.00
06:11:03     all    0.00    0.00    0.00    0.00    0.00    0.00    0.00 
100.00   1005.00

if disabled
06:13:52     CPU   %user   %nice    %sys %iowait    %irq   %soft  %steal  
%idle    intr/s
06:13:53     all    0.00    0.00    0.00    0.00    0.00    0.00    0.00 
100.00      1.00
06:13:54     all    0.00    0.00    0.00    0.00    0.00    0.00    0.00 
100.00      9.00
06:13:55     all    0.00    0.00    0.00    0.00    0.00    0.00    0.00 
100.00      4.00
06:13:56     all    0.00    0.00    0.00    0.00    0.00    0.00    0.00 
100.00      2.00
06:13:57     all    0.00    0.00    0.00    0.00    0.00    0.00    0.00 
100.00      2.00

The difference is huge, probably in power consumption too. Kernel is
relatively standard (2.6.24-rc6-git1), if required i can attach .config
If it is not bug, probably good to document, that it is killing powersaving
features?

--
Denys Fedoryshchenko
Technical Manager
Virtual ISP S.A.L.

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