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Re: launching multiple VMs takes very long time

 

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


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