VM Junkie

February 2, 2009

VROOM vs. VRC – RVI makes the difference?

Filed under: citrix, esx, vmware, xenserver — ermac318 @ 10:42 am

As has been pointed out elsewhere, there have been two very interesting sets of benchmarks that have come out in the last few weeks: Project VRC by Login Consultants, and some benchmarks from the VMware Performance Team Blog. When I first saw the discrepancy, my first thought was the same as Chris Wolf‘s, did Login Consultants enable RVI?

For those unfamiliar with RVI, or Rapid Virtualization Indexing, it’s a memory controller enhancement to make MMU-intensive workloads (like VDI or Terminal Services workloads) run much faster by doing certain operations in hardware. Generically this technology is known as Nested Page Tables. RVI is AMD’s brand name for it, Intel’s is EPT. (This is analogous to the XD/NX bit naming snafu, or the VT/AMD-V naming mess)

Back in VMworld 2006, a VMware engineer giving a talk about hardware-assisted virtualization said that this technology would have been VMware’s first choice for hardware assistance because it’s just something they computationally can’t optimize that much, it’s work that has to be done. So doing it in hardware speeds it up an awful lot. How much? VMware posted a whitepaper back in November of last year which showed a 42% improvement on standard Citrix benchmarks (and 500% on specific microbenchmarks). This is a big deal.

Which leads me to these two benchmark tests. Login Consultants did use an AMD system that supports RVI (both the servers and processors they used support it). But no where do they mention that they turned it on – in their VMware whitepaper there is no mention of “page table”, “RVI”, “NPT”, or any variation on those. Considering they felt it necessary to note they tested the advanced settings Mem.ShareScanGhz and Mem.AllocHighThreshold, my guess is they didn’t use it because it’s not enabled by default.

So next week the VROOM team says hey, this is a better test, we’ll turn RVI on and test again. And from the looks of their wording, which admittedly is a little vague, they turned it on for both hypervisors. If someone from VMware could confirm that both platforms had the benefit of RVI, that would be best.

So why doesn’t this jive with a lot of the comments I’ve been seeing about customer experience? Because as of today, RVI is off by default and worse, it’s only available on AMD processors. I think VMware cherry-picked the platform to run it on (AMD) specifically because with RVI they beat Citrix. If you install XenServer 5 and ESX 3.5u3 on an Intel System, XenServer will probably win in this particular benchmark. But, come Nehalem, ESX will pull back into the lead (because Nehalem will have Intel’s EPT technology).


1 Comment

  1. […] Check updated – RVI! Filed under: Uncategorized — ermac318 @ 6:46 pm As I noted way back when version 1.0 of Project VRC was posted, MMU virtualization technologies like AMD’s RVI and Intel’s […]

    Pingback by Project Virtual Reality Check updated – RVI! « VM Junkie — June 4, 2009 @ 6:46 pm

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