blog.vcider.com
Interrupts and context switches are now roughly the same for all three solutions. stunnel still exhibits a significantly higher CPU load (20%), but certainly does not max out the CPU anymore. I suspect that the higher numbers of context switches and interrupts result from iperf’s default behavior of sending as much data as it can in a given time interval. And since stunnel can easily compress iperf’s default data, iperf was able to send a lot of this, which also explains the results reported by iperf.
While I maintain that a setup consisting of multiple nodes is much easier to maintain with vCider – which also provides a number of other interesting features – it must be noted that stunnel does indeed perform very well for point to point connections. Note to self: Be sure not to use synthetic data for performance tests like this.
If my goal was to set up a secure tunnel, I'd be incredibly wary of using a closed source solution like this. Even if you're not worried about the government secretly demanding access to your keys, you might reasonably be concerned about vCider getting hacked.
However, I understand your concern. We are thinking of ways to address this in an even more comprehensive way.
But let's look at it. The physical link was capable of carrying something like 18 Mbit/s. When running iperf through stunnel, it reported more than 400 Mbit/s. But if you look at the actual bandwidth that was used during the transfer, it was indeed just 4.8 Mbit/s.
So, the 400 Mbit/s is clearly an illusion caused by the compression. Compressing a stream is a worth while goal, for sure. And it can be helpful in many cases. But I guess iperf's data is highly compressable. Considering that much of what's transferred these days is already compressed (multi-media files), I doubt that in the real world you will see any sort of speedup even remotely like this.
The fact is this: If it comes to actually transferring data over the wire, stunnel is very slow and there are just no two ways around it. It attempts compression at very high cost in CPU cycles and in the end is still going to be bound by context switches and interrupts.
I'm going to repeat the tests with compression disabled and update the blog post accordingly.
2. I didn't receive your email (if you really sent it).
3. Stunnel overrides the OpenSSL default of enabling compression by default since version 4.51 released over a month ago http://www.stunnel.org/?page=sdf_ChangeLog
4. Whether compression is useful or not depends on many factors, including not only type of data, but also available bandwidth and CPU power. And data compression is not an illusion. I'd be afraid to use your products if you don't understand it.
5. Compression is indeed much slower than encryption. This is a fact. Do you really mean that your product is better just because it doesn't support compression?
6. Stunnel is indeed a performance bottleneck, but only if your internet connection is over 0.5Gbps, and your server is as slow as my desktop: http://www.stunnel.org/?page=perf
2. Yes, I sent it, sorry you didn't receive it.
3. I did a standard apt-get install for stunnel on the Ubuntu Oneric system.
4. Sigh. I'm not going to comment on that one.
5. Really don't know where you would get this idea. Also don't understand why you get so upset. As I said, I was more than happy to discuss this with you ahead of time. Let me try to explain this again: I suggested that most real-world data is already compressed, thus the benefits you could derive by doing compression on the wire are lessened to the point where compression won't get you anything. For any compressable data, compressing it before sending is great and beneficial and I never stated otherwise.
I could argue whether an old Ubuntu package is "out of the box" stunnel, or whether sending 20mbit stream of compressed video is really the most common use of stunnel...
People revert to stunnel (and OpenVPN), exactly because they may not have the knowledge or inclination to get a fully featured IPSec setup going.
tinc (http://tinc-vpn.org/) would seem like a more interesting comparable than stunnel since it sets up a p2p VPN that routes all IP traffic instead of just a point-to-point link.
Tinc looks interesting, I will test that as well.
Considering the huge difference in context switches and interrupts, I don't think that encryption induced CPU load is the only issue here.
Kernel stuff on its own doesn't just magically run faster, of course. But in this case, I think it's the constant interaction between user-space and kernel-space, which causes the problem. That's an issue that will impact any user-space solution to a networking problem.
Can 1200 extra context switches and ~6400 extra interrupts per second use up 100% cpu? In fact you mention that for stunnel most of the CPU was in userspace and not the kernel which would indicate time spent actually using the CPU instead of doing context-switches and interrupts, which I assume top would show as "sys".
I also find the extra interrupts strange. I wonder if vCider is sending bigger packets and what caching/latency implications that might have.
stunnel tries to compress traffic as well, which works if you send a lot of stuff that isn't already compressed. But most of what's sent these days (multi-media?) already is encrypted, so this will be a wasted effort.