Building a High-Performance Cluster with Gentoo [LWN.net]

Building a High-Performance Cluster with Gentoo

Posted Apr 11, 2007 0:09 UTC (Wed) by drag (subscriber, #31333)
Parent article: Building a High-Performance Cluster with Gentoo

Well it's obvious now.

We want benchmarks from the Gentoo community to make sure that it's worth our time to even give a crap about doing oddball compiler optimizations on a kernel or glibc as well as the rest of the OS.

I'd like to see a comparisions between Debian (cold) vs Fedora (warm) vs highly optimized Gentoo (hot) on identical hardware running:

1. Filesystem benchmarks.
2. network I/O benchmarks.
3. computational benchmnarks.
4. database bencmarks.
5. application benchmark.
(Stuff like rendering 3d scenes, data encoding, compiling and such stuff. to illistrate the impact that benchmarks may have on real world use)

Just like the sort of stuff you'd find on any reputable hardware-oriented website trying to compare motherboards or cpus.

If anybody can do that and come away with conclusive evidence that all that time spent on Gentoo is actually worth anything then I'd find that a very compelling reason to use Gentoo.

But so far anything I've seen actually points that people playing around with optimizations often actually _reduce_ performance and increase bugginess. So not only you end up wasting your time compiling everything, but your actually making slower.

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Building a High-Performance Cluster with Gentoo

Posted Apr 11, 2007 10:06 UTC (Wed) by drag (subscriber, #31333) [Link]

Ya and with that it shown that Gentoo compiled with 'optimizations' was slower then both Debian and Mandrake most of the time.

Of course this is old and with GCC 3.xx stuff. GCC 4.xx is a entirely different beast.

I think it's simply fair to compare whatever latest release of whatever distribution you plan on using and whatever software comes with it, more or less.

Historically speaking when your presented with vague claims by any software vendor of improved performance, but fails to back it up with facts.. then the vast majority of the time they were just mostly full of it.

I know that compile time optimizations can be counter intuitive in a lot of cases. The biggest example I know of is that the Linux kernel has best performance when compiled optimized for size, not for speed.

This is because when you optimize for speed you end up with larger binaries and larger logical steps. When compiled for size, the logic it tighter and the binaries are smaller. With this sort of setup more of the kernel runs in CPU cache and your CPU is going to spend less time retrieving kernel bits from main memory and more time actually processing.

So it's all a bit weird. I am sure that that isn't the only time compiling something -0s or -0 would end up faster then -03.

Building a High-Performance Cluster with Gentoo

Posted Apr 11, 2007 20:06 UTC (Wed) by job (guest, #670) [Link]

It all boils down to if you trust the package maintainer to select the best compiler optimizations or if you believe you can select better general ones. Many maintainers are highly competent people and the data seems to support that.

Of course, rebuilding packages from source is really simple in Debian too, so it's not really only distribution dependent.

That said, most Gentoo people probably use the distribution because the build flags are quite handy, not because of some imaginary performance benefits.

Building a High-Performance Cluster with Gentoo

Posted Apr 11, 2007 21:08 UTC (Wed) by lorien420 (guest, #44036) [Link]

I use Gentoo. Originally it was the dream of performance benefits that drew me to it because I never have a lot of money and am always about three years behind on the greatest-bang-for-the-buck hardware.

I can't honestly say whether Gentoo has ever given me any performance benefits. In the end, I've discovered that I don't care. I use Gentoo because it's constantly building from source. A lot of free software is about having the sources and the freedom to do what I want to with them. Gentoo's portage system is a massive archive of sources and the hoops you have to jump through to build them.

That's the advantage to me. I have all of the software on my computer installed with instructions to help me tweak it if I want to.

Building a High-Performance Cluster with Gentoo

Posted Apr 12, 2007 1:33 UTC (Thu) by dw (subscriber, #12017) [Link]

Thank you. This is the first time since Gentoo appeared that I've read what appears to be both an honest testimonial and a practical use for the system.

Having worked on commercial software for Linux in the past, I often found myself rebuilding complex trees (e.g. Mozila, wxWidgets) just to flip one or two extra flags (Unicode on/off? --some-strange-chunk-of-code=yes). It was more often than not, easier to do this by just grabbing the original .tar.gz rather than doing a deb or rpm source build. In retrospect, Gentoo may have saved me a lot of pain and trouble in those days.

Building a High-Performance Cluster with Gentoo

Posted Apr 22, 2007 22:41 UTC (Sun) by dlang (✭ supporter ✭, #313) [Link]

the performance benifits of gentoo are going to vary wildly depending on your hardware.

back in the days of the 1GHz Athlon, the distros were all compiling their code for 386's (with a few just starting to offer 586 optimized versions) the optimizations for AMD chips were significantly different then for Intel chips

in that environment there is room for a HUGE performance difference from a simple recompile, and that's when gentoo started (and so I'm sure that's part of where the proponents are looking when they talk about the speed benifits)

however, even on modern 64 bit systems that haven't been out long enough to develop this much variability there are compile options for packages that can make a huge performance difference to your apps

a perfect example is unicode support. if you need it, you need it, no question. but if all the data you are dealing with is ascii the performance difference between comiling with and without unicode support can be drastic (I see 2x and more on the postgres performance list) these are the comile flags that make the most difference nowdays.

In addition, just being able to not include features that you don't need for your installation is a huge benifit. Last week I built a new debian system, when I installed the ftp software it pulled in mySQL libraries, when I installed telnet it pulled in gcc. now in the case of telnet I found that I could go back and remove most of gcc (most of it was reccomended dependancies, not required), but on a gentoo system you just define -mysql and you won't have software installing mysql for you (I still haven't figured out why telnet requires the gcc libs yet)

Building a High-Performance Cluster with Gentoo

Posted Apr 23, 2007 9:44 UTC (Mon) by pimlottc (guest, #44833) [Link]

Are you sure that the actual GCC compiler was installed?

Looking at the telnet package, it does depend on two gcc runtime libraries, libgcc1 and libgcc4. Each of these depend on gcc-4.1-base, which sounds a lot like it's the main gcc package, but in fact it's just licensing ibnformation and packaging documention.

I can't find anything in telnet's dependency tree that depends on or recommends the actual gcc package (which is simply gcc). Recommends aren't normally automatically installed by apt-get, although I don't know for sure about other package management front ends.