Scaling up your virtualization solution on 8-socket HP ProLiant Servers
These days, when wearing my “Linux planner” hat, and with Virtualization being the “phrase that pays”, I’m often asked to help provide guidance on how to best take advantage of the technology included in our 8-socket HP ProLiant server offerings for Linux based virtualization solutions like Red Hat Enterprise Virtualization or Suse Linux Enterprise Server Xen (there’s a plethora of information out there about VMware ESX/ESXi 3.5.x and vSphere 4.0, so I’m not going to talk about that, this time around.)
The problem I’ve had, until recently, was providing actual – objective - data as a means to help illustrate my points. For instance, I could not clearly illustrate how a snoop filter on the CPU interconnect can improve the linearity of the workload scalability in a virtualized environment (see Fig. 1).
Fig. 1: Average response time with pinned vs. un-pinned processors
I was unable to demonstrate benefits of the NUMA aware scheduler that the Linux kernel uses and how it does improve performance. (In figures 2 and 3, it’s represented by the improvement in average response times from the web-servers included in the workload) when your workloads run with memory interleaving disabled in the system BIOS – see Fig. 2. Unless, for support reasons, your application vendor explicitly tells you otherwise.
Fig. 2: Average Response Times - Non-interleaved Memory Config
Fig. 3: Average Response Times - Interleaved memory
I also used to have a hard time explaining how and why to tune the Linux kernel for these systems. For instance, I only suspected how little (none) tuning of the host platform is required in order to drive pretty significant numbers of guests (98) in these environments - see Fig. 4. But, if you engage in some very minor tuning activities of the network stack, how those very same workload performance results can be extended even further (to 256 guests) – see Fig. 5:
Fig. 4: The system has not been tuned beyond it's "out of the box" state.
Fig. 5: System is tuned and exhibiting linear scalability to 256 KVM guests
As part of a joint documentation effort with Red Hat, all of the data collected has been brought together in a Reference Architecture document - “Scaling RHEL 5.4 + KVM up to 256 Guests" available for free from Red Hat’s website.
We obviously picked the guest density to prove a point about the platform, however it’s worth mentioning that 256 guests does not represent the upper bound for the platform. It only represents where we thought the density went (far) beyond what is reasonable to expect in a production environment this day in age.
Contributed by Thomas Sjolshagen (Strategic Planner for Linux and Virtualization on scale-up x86 servers)
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- Contributed by John Rinehart
