linux-kernel - High sleep_on

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Message-ID: <CAKwxwqwM0usOqvbu8ZaG6=SXS6tjQXqtrGjXnbEUMuqZaUs8Sg@mail.gmail.com>
Date:	Mon, 16 Jan 2012 10:18:10 +0530
From:	Prateek Sharma <prateek3.14@...il.com>
To:	Linux Kernel <linux-kernel@...r.kernel.org>,
	kernelnewbies@...nelnewbies.org
Subject: High sleep_on_page latency

Hello,
  I am measuring system latency using latencytop. I am using kernel
version 3.0 with some minor changes.
The latencytop output for the process doing the IO (qemu) is below:

Process qemu-system-x86 (6239)             Total: 31363.7 msec
[sleep_on_page]                                   1966.5 msec         81.4 %
Waiting for event (select)                          5.0 msec          7.8 %
[kvm_vcpu_block]                                    5.0 msec          8.5 %
synchronous write                                   1.7 msec          0.0 %
Userspace lock contention                           1.5 msec          2.3 %

Is the 2000 msec sleep_on_page delays normal ? I would also like to
know what sleep_on_page exactly corresponds to. My understanding is
that it is the time spent waiting for grabbing a lock on a page. Is
this correct ?

Thanks.
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