NO_HZ and cpu monitoring tools

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From: Anton Blanchard <anton@...>

To: <mingo@...>, <tglx@...>

Cc: <linux-kernel@...>

Subject: NO_HZ and cpu monitoring tools

Date: Sunday, October 14, 2007 - 7:42 pm

Hi,

When using a NO_HZ kernel on ppc64, I noticed top gives some interesting
results:

Cpu0 : 0.0%us, 0.0%sy, 0.0%ni,100.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu1 : 0.0%us, 0.0%sy, 0.0%ni, 0.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu2 : 0.0%us, 0.0%sy, 0.0%ni, 0.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu3 : 0.0%us, 0.0%sy, 0.0%ni, 0.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu4 : 0.0%us, 0.0%sy, 0.0%ni, 0.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu5 : 1.1%us, 0.0%sy, 0.0%ni, 98.9%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu6 : 0.0%us, 0.0%sy, 0.0%ni, 0.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu7 : 0.0%us, 0.0%sy, 0.0%ni, 0.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st

Notice how only 2 cpus report idle time. Im guessing this happens if
a core sleeps for longer than the update period in top. Where should
this be fixed?

It would be possible for the proc read method to add in the right number
of idle jiffies, or top could just assume no increment means 100% idle.

Anton
-


linux-kernel:
Mark Lord	2.6.25-rc8: FTP transfer errors
Kamalesh Babulal	Re: 2.6.23-rc6-mm1
Greg Kroah-Hartman	[PATCH 025/196] paride: Convert from class_device to device for block/paride
Stephen Rothwell	Announce: Linux-next (Or Andrew's dream :-))
git:

linux-netdev:
Linus Torvalds	Re: iptables very slow after commit 784544739a25c30637397ace5489eeb6e15d7d49
David Miller	Re: [GIT]: Networking
Gerrit Renker	[PATCH 18/37] dccp: Support for Mandatory options
Jarek Poplawski	[PATCH] pkt_sched: Destroy gen estimators under rtnl_lock().
openbsd-misc:

NO_HZ and cpu monitoring tools

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