linux-kernel - strange values of loadavg and nr of io-blocked tasks

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Message-ID: <20121116114703.GA8634@pcnci.linuxbox.cz>
Date:	Fri, 16 Nov 2012 12:47:03 +0100
From:	Nikola Ciprich <nikola.ciprich@...uxbox.cz>
To:	linux-kernel mlist <linux-kernel@...r.kernel.org>
Cc:	nik@...uxbox.cz
Subject: strange values of loadavg and nr of io-blocked tasks

Hi,

I was doing some I/O tuning of our KVM host, and noticed some
strange behaviour. When I start some heavy I/O load on guest
(ie run some fio benchmark), loadavg value of the host jumps
to value about 65 and holds until load ends. sar reports similar
number of blocked tasks. I don't really understand those numbers,
because only active tasks are 4 qemu-kvm threads and few other sleeping
tasks (so none in R or D state).
is it possible to somehow find which tasks seem to be blocked?
or why is loadavg value so high?
the system is x86_64 quad core with 4GB RAM running centos 6 with 3.0.52-rc1 kernel.

Thanks a lot in advance for any answer

BR

nik

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