Daily Archives: June 18, 2013

The Funny KVM benchmarks

RedHat Summit 2013 concluded recently and while browsing some of the presentation PDFs I came across something funny. In general the content is good and there is a bunch of interesting stuff available. However this particular PDF ruffled me up: http://rhsummit.files.wordpress.com/2013/06/sarathy_t_1040_kvm_hypervisor_roadmap_and_overview.pdf

This presentation talks about KVM technology in general with a bunch of marketing content thrown in which is all fine. However fast forward to slide 12 and something looks odd. The slide seems to scream KVM’s outstanding performance on SPECvirt_sc2010 as compared to ESXi5/4. Great isn’t it ? The “Eureka” feeling lasts till you look at the bottom of the graphs. Every comparison is done on dissimilar hardware! Suddenly Archimedes comes crashing to the floor.

Take for example the 2-socket 16-core benchmarks. The HP DL385 G7 box is a Generation 7 AMD bulldozer piece while DL380p Gen8 is a Generation 8 Sandy Bridge piece. RedHat is putting ESXi5 on an older generation hardware and KVM on the latest, greatest. If we consider the highest bin processors then the DL385 will get AMD Opteron 6220, 3.0 GHz processors with 16MB cache while DL380p will get Xeon E5-2690, 2.9 GHz processors with 20MB cache. Even if the Opteron’s clock is marginally higher a Bulldozer is simply no match for a big juicy Sandy Bridge beast. Second the Bulldozers get HT links with 6.4 GT/s throughput while the Xeons get QPI with 8 GT/s throughput. The Gen7 box gets PCIe Gen 2.0 while Gen 8 boxes get PCIe Gen 3.0. Similarly the story goes on and on. So we have a no-contest here. The Gen8 box wins hands down even if one puts fewer VMs on the Gen7 box.

Let’s look at the 4-socket 40 cores comparo. First the two boxes are from two different vendors. Second they are comparing ESXi4.1 with latest KVM. Whatever happened to ESXi5 here ? Does it not support that hardware ? At least the processors on the two boxes IBM x3850 x5 and DL580 G7 are comparable 10-core Xeon E7-4870 ones (considering the highest bin 10-core processors). However older ESX version skews the game.

Similarity the processors on the other comparisons are similar but the ESX version is older one that everyone is migrating off. If I am going to do a comparison, I will install latest ESX on a hardware, measure, reinstall latest KVM on the same hardware and measure not play games.

RedHat is nonchalantly tying one hand behind ESX’s back. Helpfully for the marketing fuzz types we have this fine print at the bottom: “Comparison based on best performing Red Hat and VMware solutions by cpu core count published at http://www.spec.org”. That is we are going by earlier measurements that our competitors published, so everyone chant after us: KVM is faster than ESX, KVM is faster than ESX, KVM is faster than ESX … ah well, let me grab that can of Diet Coke sitting nearby (or should it be salt rather?).


I am NOT a Linux or KVM hater. On the other hand I use Linux Mint day in and day out and work with open-source in general. However above all I am a technologist and I like to take things as they really are, free of all the fuzz. Fuzz dilutes the values that various technologies bring to the table.