<html>
<head>
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
</head>
<body text="#000000" bgcolor="#CCCCCC">
<div class="moz-cite-prefix">
<div class="moz-cite-prefix">On 01/07/2015 04:32 PM, Tim Bell
wrote:<br>
</div>
<blockquote
cite="mid:5D7F9996EA547448BC6C54C8C5AAF4E50102632B85@CERNXCHG41.cern.ch"
type="cite">
<blockquote type="cite" style="font-style: italic; color:
#000000;">
<pre wrap=""><span class="moz-txt-citetags">> </span>The profile of this hardware looks virtualized. That makes me ask if you have
<span class="moz-txt-citetags">> </span>installed the para-virtualized drivers ?
<span class="moz-txt-citetags">> </span>
</pre>
</blockquote>
<pre wrap="">Out of interest, does using para-virtualized drivers reduce the chance of soft lockups ? I can understand that it is more efficient but I do not know if the soft lockups are more likely when using emulated hardware.</pre>
</blockquote>
<br>
Please see below for more details. You have a high change to run
into soft lockups if you have no CPU cycles available. When I/O
intensive tasks run, most of your CPU cycles are blocked
contending to get an ack for the write() call.<br>
<br>
<br>
On 01/07/2015 04:43 PM, Matej Mailing wrote:<br>
</div>
<blockquote
cite="mid:CAF44DZcx6OzJ0V9mNukMLGM1SgLK8Ox-NWYU0fYvQNgiUH1QaQ@mail.gmail.com"
type="cite">
<pre wrap="">Hi, we are using virtio
<target dev='vda' bus='virtio'/>
(from the instance's xml on the compute node)
Should we use any particular other drivers on the instance as well?</pre>
</blockquote>
<br>
No. You should always use virtio drivers for both, network and
block.<br>
<br>
But, your CPU consumptions were still blocked. My initial suspicion
was that they were blocked because you weren't using virtio drivers.
When you don't use virtio drivers, the Host OS spends more time in
translating the instructions. By using virtio, you instruct right
inside the Guest OS, the capabilities of the Host OS and the
underlying physical hardware. Thus resulting is much better
performance.<br>
<br>
That said, since you are using virtio for both net/block, it would
be interesting to determine the cause of your setup. What kind of
backend storage do you have ? What is the latency on it ?<br>
<br>
It could genuinely be one of the following case:<br>
<br>
* Slow storage<br>
* Slow storage driver (can be knocked off, given that you confirmed
you use virtio)<br>
* Memory contention - If you do too much buffered I/O, without
writing the dirty pages back.<br>
<br>
<br>
PS: It'd be easier if you pasted your logs, formatted, somewhere
else. The mail client screws up the logs completely. :-(<br>
<br>
<pre class="moz-signature" cols="72">--
Ritesh Raj Sarraf
RESEARCHUT - <a class="moz-txt-link-freetext" href="http://www.researchut.com">http://www.researchut.com</a>
"Necessity is the mother of invention."
</pre>
</body>
</html>