The Virtualization Benchmarking Chaos

There are an incredible number of pitfalls in the world of server application benchmarking, and virtualization just makes the whole situation much worse. In this report, we want to measure how well the CPUs are coping with virtualization. That means we need to choose our applications carefully. If we use a benchmark that spends very little time in the hypervisor, we are mostly testing the integer processing power and not how the CPU copes with virtualization overhead. As we have pointed out before, a benchmark like SPECjbb does not tell you much, as it spends less than one percent of its time in the hypervisor.

How is virtualization different? CPU A that beats CPU B in native situations can still be beaten by the latter in virtualized scenarios. There are various reasons why CPU A can still lose, for example CPU A…

  1. Takes much more time for switching from the VM to hypervisor and vice versa.
  2. Does not support hardware assisted paging: memory management will cause a lot more hypervisor interventions.
  3. Has smaller TLBs; Hardware Assisted Paging (EPT, NPT/RVI) places much more pressure on the TLBs.
  4. Has less bandwidth; an application that needs only 20% of the maximum bandwidth will be bottlenecked if you run six VMs of the same application.
  5. Has smaller caches; the more VMs, the more pressure there will be on the caches.

To fully understand this, it helps a lot if you read our Hardware Virtualization: the nuts and bolts article. Indeed, some applications run with negligible performance impact inside a virtual machine while others are tangibly slower in a virtualized environment. To get a rough idea of whether or not your application belongs to the latter or former group, a relatively easy rule of thumb can be used: how much time does your application spend in user mode, and how much time does it need help from the kernel? The kernel performs three tasks for user applications:

  • System calls (File system, process creation, etc.)
  • Interrupts (Accessing the disks, NICs, etc.)
  • Memory management (i.e. allocating memory for buffers)

The more work your kernel has to perform for your application, the higher the chance that the hypervisor will need to work hard as well. If your application writes a small log after spending hours crunching numbers, it should be clear it's a typical (almost) "user mode only" application. The prime example of a "kernel intensive" application is an intensively used transactional database server that gets lots of requests from the network (interrupts, system calls), has to access the disks often (interrupts, system calls), and has buffers that grow over time (memory management).

However, a "user mode only" application can still lose a lot of performance in a virtualized environment in some situations:

  • Oversubscribing: you assign more CPUs to the virtual machines than physically available. (This is a very normal and common way to get more out of your virtualized server.)
  • Cache Contention: your application demands a lot of cache and the other virtualized applications do as well.

These kinds of performance losses are relatively easy to minimize. You could buy CPUs with larger caches, and assign (set affinity) certain cache/CPU hungry applications some of the physical cores. The other less intensive applications would share the CPU cores. In this article, we will focus on the more sensitive workloads out there that do quite a bit of I/O (and thus interrupts), need large memory buffers, and thus talk to the kernel a lot. This way we can really test the virtualization capabilities of the servers.

Index Independent Real-World Virtualization Benchmarking


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  • tshen83 - Thursday, May 21, 2009 - link


    Let's not fool each other. Johan's AMD bias is disgusting.

    My assertion that HardOCP killed the GPU market is simply trying to show you the effect of invalidating industry standard benchmarks. Architecturally, Nvidia's GPU bigger monolithic cores are far more advanced than ATI's cores right now. In GPGPU applications, it is not even close. The problem with gaming FPS benchmark as I have said is that developers are typically happy once the FPS reaches parity. It does not show architectural superiority.

    vApus? There are a ton of questions unanswered.
    1. Who wrote the software?(I assume European)
    2. Does the software scale linearly? And does the software scale on both AMD and Intel architecuture?
    3. Why benchmark 4 Core Virtual machines when we know that VMware doesn't really scale that well themselves in SMP setup?
    4. Seriously? OLAP database? How many real world people run

    I usually don't respond to Anandtech articles unless the article is disgustingly stupid. I also don't understand why you guys can't accept the fact that Nehalem is in fact 100% performance/watt improved vs the previous generation Xeon. It is backed by data from more than one industry standard benchmark.

    Is AMD worth a look today? No, absolutely not. If you are still considering anything AMD today, you are an idiot. (The world is full of idiots) AMD's only chance is if they can release the G34 socket platform within a TDP range that is acceptable before they run out of cash.

    Before you call me a troll, remind yourself this: usually the troll is smarter than the people he/she is trolling. So ask yourself this question: did Johan deserve the negative critism?
  • JarredWalton - Thursday, May 21, 2009 - link

    You criticize every one of his articles, often because I'm not sure your reading comprehension is up to snuff. His "AMD bias" is not disgusting, though I'm quite sure your Intel bias is far worse than his AMD bias. The reason 3DMark has been largely invalidated is that it doesn't show realistic performance - though some of the latest versions scale similarly to some games, at best 3DMark measures 3DMark performance. Similarly, VMmark measures VMmark performance. Unless your workload is the same as VMmark, it doesn't really tell you much.

    1 - Who wrote the software? According to the article, "vApus or Virtual Application Unique Stresstest is a stress test developed by Dieter Vandroemme, lead developer of the Sizing Server Lab at the University College of West-Flanders." His being European has nothing to do with anything at all, unless you're a racist, bigoted fool.

    2 - 2-tile and 3-tile testing is in the works. It will take time.

    3 - Perhaps because there are companies looking for exactly that sort of solution. I guess we should only test situations where VMware performs optimally?

    4 - The source of the database is not so critical as the fact that it is a real-world database. Whether Johan uses a DB from,,, or some other source isn't particularly meaningful. It is a real setup used outside of benchmarking, and he had access to the site.

    I usually don't respond to trolls unless they are disgustingly stupid as well. I don't understand why you can't accept the fact that Nehalem isn't a panacea that fixes all the world's woes. That is backed by the world around us which continues to have all sorts of problems, and a "greener" CPU isn't going to save the environment any more than unplugging millions of cell phone charges that each consume 0.5W of power or less.

    AMD is certainly worth a *look* today. Will you actually end up purchasing AMD? That depends largely on your intended use. I have old Athlon 64/X2 systems that do everything that they need to do. For a small investment, you can build a much better AMD HTPC than Intel - mostly because the cheap Intel platform boards are garbage. I'd take a lesser CPU with a better motherboard any day over a top-end CPU with a crappy motherboard. If you want a system for less than $300, the motherboards alone would make me tend towards AMD.

    Of course, that completely misses the point that this isn't even remotely related to that market. Servers are in another realm, and features and support are critical. If you have a choice between AMD quad socket and Intel dual socket, and the price is the same, you might want the AMD solution. If you have existing hardware that can be upgraded to Shanghai without changing anything other than the CPU, you might want AMD. If you're buying new, you'd want to look at as much data as possible.

    Xeon X5570 still surpasses AMD in the initial tests by over 30%, which is not insignificant. If that extends to 50% or more in 2-tile and 3-tile setups, it's even more in Intel's favor. However, a 30% advantage is hardly out of line with the rest of the computing world. SYSmark 2007 shows the i7 965 beating the Phenom II 955 by 26.6%. Photoshop CS4 shows a 48.7% difference. DivX is 35.3%, xVid is 15.9% pass1 and 65.4% pass2, and WME9 is 25%. 3dsmax is 55.8%, CINEBENCH is 42%, and POV-ray is 65.3%.

    Which of those tests is a best indication of true potential for Core i7? Well, ALL OF THEM ARE! What's the best virtualization performance metric out there? Or the best server benchmark out there? They're ALL important and useful. vApus is just one more item to look at, and it still shows a good lead for Intel.

    Where is the 100% perf/watt boost compared to last generation? Well, it's in an application where i7 can stretch its eight threaded muscles. Compared to AMD, the performance/watt benefit for an entire system is more like 40% on servers. For QX9770, i7 965 is 32% more perf/watt in Cinebench, or 37.6% in Xvid. I doubt you can find a 100% increase in performance/watt without cherry-picking the benchmark and CPUs in question, but that's what you're already determined to do. That, my friend, is true bias - when you can't even admit that anything from the competition might be noteworthy, you are obviously wearing blinders.
  • Zstream - Thursday, May 21, 2009 - link

    Umm based on your two rants this means you have ZERO knowledge working with virtual desktops/terminal servers/virtual applications.

    I feel I need to make two corrections.

    One: ATI's die size is roughly 75% of Nvidia's, how do you conclude that Nvidia is better? Well honestly you can not because if you scale the performance and had the same die size of Nvidia, then ATI would be killing them.

    Second: Majority of enterprise's run AMD and Intel, in fact not till Neh. did Intel really come into the virtualization market.
  • tshen83 - Thursday, May 21, 2009 - link

    "Umm based on your two rants this means you have ZERO knowledge working with virtual desktops/terminal servers/virtual applications. "

    Really? Just how did you come up with this revelation?

    "One: ATI's die size is roughly 75% of Nvidia's, how do you conclude that Nvidia is better? Well honestly you can not because if you scale the performance and had the same die size of Nvidia, then ATI would be killing them. "

    You don't know shit about GPUs.

    "Second: Majority of enterprise's run AMD and Intel, in fact not till Neh. did Intel really come into the virtualization market. "

    True. That's what I am saying too, if you listened. I said, "no one should be considering AMD today because Nehalem is here".
  • Zstream - Thursday, May 21, 2009 - link

    I came to that conclusion based on your incoherent rants.

    Why would you say I do not know shit about GPU's? I provided you a fact, your illogical thinking does not change the matter. It comes down to die size and ATI wins performance/DIE. If you would like to argue that claim with then please do so.

    Who would consider Neh in todays market? Very few, unless you are a self proclaimed millionaire who crazily spends or needing the extra performance boost in some applications like exchange.
  • Viditor - Thursday, May 21, 2009 - link

    Guys, it's tshen...nobody over the age of 12 listens to his rants anyway, so don't feed the troll (or ban him if you can...). Reply
  • leexgx - Thursday, May 21, 2009 - link

    LOL nice rant

    3dmark cant be used any more as its not an 3dmark any more its more like an 3d gpu/cpu mark the CPU can sway the total result

    AMD cpus have been using dedicated bus that talks to each other cpu socket and has direct access to the ram, allso AMD does have V-amd as well on all amd64 am2 cpus as well as optrons an (baring sempron)
  • Makaveli - Thursday, May 21, 2009 - link

    Ya what is the post all about.

    HardOCP killed the GPU market? I don't know about you but I never bought a videocard because of its 3dmark score. It's one benchmark that both companies cater to but is of little importance. Hardocp review method has much more valuable data for me than one benchmark.

    Let me ask you this when you are buying a car or anything of siginicant value. Do you not do your homework is one review being either positive or negative enough to drop your hard earned cash?

    If so Bestbuy is that way!

    As for the rest of your post the personal attacks and childish language cleary show your not even worth taking seriously. Sounds more like the ramblings of a Highschool child who is trying to get attention.

    Good day to you sir,

  • Zstream - Thursday, May 21, 2009 - link

    You have no idea what you are talking about. The benchmark software can be downloaded. It is not our fault you are to poor to pay for a product.

    The rest I have to say "LOL".
  • DeepThought86 - Thursday, May 21, 2009 - link

    Wow, just wow. Reply

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