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On 01/07/2015 04:32 PM, Tim Bell wrote:
>> > The profile of this hardware looks virtualized. That makes me ask if you have
>> > installed the para-virtualized drivers ?
>> > 
> 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.

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.


On 01/07/2015 04:43 PM, Matej Mailing wrote:
> 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?

No. You should always use virtio drivers for both, network and block.

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.

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 ?

It could genuinely be one of the following case:

* Slow storage
* Slow storage driver (can be knocked off, given that you confirmed you
use virtio)
* Memory contention - If you do too much buffered I/O, without writing
the dirty pages back.


PS: It'd be easier if you pasted your logs, formatted, somewhere else.
The mail client screws up the logs completely. :-(

-- 
Ritesh Raj Sarraf
RESEARCHUT - http://www.researchut.com
"Necessity is the mother of invention."

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