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Hardware Virtualization Slower Than Software?
Jim Buzbee writes "Those you keeping up with the latest virtualization techniques being offered by both Intel and AMD will be interested in a new white paper by VMWare that comes to the surprising conclusion that hardware-assisted x86 virtualization oftentimes fails to outperform software-assisted virtualization. My reading of the paper says that this counterintuitive result is often due to the fact that hardware-assisted virtualization relies on expensive traps to catch privileged instructions while software-assisted virtualization uses inexpensive software substitutions. One example given is compilation of a Linux kernel under a virtualized Linux OS. Native wall-clock time: 265 seconds. Software-assisted virtualization: 393 seconds. Hardware-assisted virtualization: 484 seconds. Ouch. It sounds to me like a hybrid approach may be the best answer to the virtualization problem.
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See title... VMWare make software virtualisation products. Of course they're going to try and find that software methods are better.
I drink to make other people interesting!
* - I imagine in real life it's not a 1:1 ratio, but for the sake of argument, work with me.
Clones are people two.
The correct conclusion is not that virtualization is better done entirely in software, but that current hardware assists to virtualization are badly designed. As the complete article points out, the hardware features need to be designed to support the software - not in isolation.
It reminds me of an influential paper in the RISC/CISC debate, about 20 years ago. Somebody wrote a C compiler for the VAX that output only a RISC-like subset of the VAX instruction set. The generated code ran faster than the output of the standard VAX compiler, which used the whole (CISC) VAX instruction set. The naive conclusion was that complex instructions are useless. The correct conclusion was that the original VAX compiler was a pile of manure.
The similarity of the two situations is that it's a mistake to draw a general conclusion about the relative merits of two technologies, based on just one example of each. You have to consider the quality of the implementations - how the technology has been used.
I suppose there are certain things hardware virtualisation does better.
The trick is, I'd guess, to find out which works better in which circumstances.
You see that people suspect this white paper because of its origin; they are right in doing so at least because only one type of test has been performed; surely not all computing tasks perform the same way as a kernel compile.
This suggests that VMWare have found the example which supports their claims the best; the question is, of course, whether this is the only such example.
So if we suppose that there are certain types of problems where hardware virtualisation outperforms software virtualisation, hybrid solutions seem to be the right way to go.
P.S. I don't really know what I'm talking about...
Ignore this signature. By order.
When are people going to figure out that "hardware solutions" are really software running on hardware, just like any other solution?
Sure, the instructions may be hardcoded, coming out of ROM, or whatever, but in the end its instrructions that tell the hardware what to do. And those instructions are called "software", no matter how the vendor tries to spin it. And if the solutions performs badly, it is because the software is designed badly. Period.
You aren't remembered for doing what is expected of you
Insisting on third-party verification of results is hardly damning either of them... It's just scientific. You (and everyone else) are absolutely right to be sceptical, and not just because VMware have a vested interest in this case. They might just be wrong. Or not.
Reality is the ultimate Rorschach.
Hardware virtualization may be slower right now, but both the hardware and the software supporting it are new. Give it a few iterations and it will be equal to software virtualization.
It may or may not be faster eventually, but that doesn't matter. What matters is that small changes in the hardware make it possible to stop having to depend on costly, proprietary, and complex software--like that sold by VMware.
I don't see how that tracks. How is the %2 impact going to save me a bundle? Moving to linux suposedly will save me money if I virtualize or not, don't see how it being virtualization friendly improves things. Are you saying I'll spend less in hardware by switching to linux? Migrating to linux isn't free (man-hours wise), so the hardware savings better be pretty damn substantial to offset it.
I should be sleeping.
Rich
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Because if you actually RTFA it shows that the hardware virtualization is faster for some benchmarks (e.g. processing system calls) and slower for others (e.g. performing I/O requests or page-table modifications); if you combine the best features of each you should be able to get a virtual machine that is faster than both.
It's not that people don't look to old mainframe solutions for things, they do, it's that often what was feasable on those wasn't on normal hardware, until receantly. There was no reason for chip makers to waste silicon on virtualization hardware on desktops until fairly receantly, there just wasn't a big desktop virtualization market. Computers are finally powerful to the point that it's worth doing.
It's no supprise that large, extremely expensive computers get technology before home computers do. You give me $20 million to build something with, I can make it do a lot. You give me $2000, it's going to have to be scaled way back, even with economies of scale.
You see the same thing with 3D graphics. Most, perhaps even all, the features that come to 3D cards were done on high end visualizaiton systems first. It's not that the 3D companies didn't think of them, it's that they couldn't do it. The orignal Voodoo card wasn't amazing in that it did 3D, it was much more limited than other thigns on the market. It was amazing in that it did it at a price you could afford for a home system. 3dfx would have loved to have a hardware T&L engine, AA features, procedural textures, etc, there just wasn't the silicon budget for it. It's only with more developments that this kind of thing has become feasable.
So I really doubt Intel didn't do something like VT because they thought IBM was wrong on the 360, I think rather they didn't do it because it wasn't feasable or marketable on desktop chips.
So in what way is it different for VMWare? It also is free! And in addition lets you run unmodified kernels.