openstack team mailing list archive

[Rick Jones <rick.jones2@xxxxxx>]

On 04/30/2013 01:36 PM, Melanie Witt wrote:
> This presentation from the summit might be of interest to you:
>
> http://www.openstack.org/summit/portland-2013/session-videos/presentation/scaling-the-boot-barrier-identifying-and-eliminating-contention-in-openstack

A nice presentation.  Based on his comment at the end, I did the web 
search and found his slides at:

http://www.cs.utoronto.ca/~peter/feiner_slides_openstack_summit_portland_2013.pdf

A caveat/nit/whatnot about looking at overall system CPU utilization and 
assuming no CPU bottleneck (the "hardware" portion at the beginning) at 
points even well below 100% utilization - with multiple CPUs in a system 
now, there are for example, many ways for there to be 50% overall CPU 
utilization.  It could be that all the CPUs are indeed at 50% util, but 
it could also be that 1/2 the CPUs are at 100% and the other half are 
idle.  Now, perhaps that fits in the space between a hardware and a 
software bottleneck, but I'd be cautious about overall CPU utilization 
figures.

For example, a single or small number of CPUs saturating can happen 
rather easily in some "networking" workloads - the CPU servicing 
interrupts from the NIC (or CPUs if the NIC is multiqueue) can saturate. 
 I'd consider that a hardware saturation, even though many of the other 
CPUs in the system are largely idle.  That is why in later versions of 
netperf, there is a way to report the ID and utilization of the most 
utilized CPU during a test, in addition to reporting the overall CPU 
utilization.

rick jones