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Two papers On Performance Tuning FreeBSD
avleenvig writes "Finally I have completed my paper on tuning the FreeBSD system for various common tasks, to compliment the paper on compiling and tuning the FreeBSD kernel. These papers were written against FreeBSD 4.x systems but should be equally applicable to 5.x systems on almost all counts. Compiling and tuning the FreeBSD kernel:
http://silverwraith.com/papers/freebsd-kernel.php
Performance tuning FreeBSD for different applications:
http://silverwraith.com/papers/freebsd-tuning.php. You will find within, details on tuning your network, disks, sysctls and kernel for maximum performance under various conditions. "
But if you ever had analysed *nix systems for performance bottle necks this could only help for some little problems.
If he had read the tuning(7) man page, there would be more information for other parts of the system.
But he had done that what I didn't: put up a website with informations for anybody. So overall: Great Work!
Thanks for the good word :-)
I tried hard to cover things not mentioned in tuning(7). That page alreasdy has a lot of good stuff in it that I couldn't really improve.
I felt there was something missing though and when I first started performance tuning I found that the data I've written about isn't in one single location.
Of course, I'll keep adding to it as I learn more.
Hopefully in the next week I'll have a paper up on what you can do to your server to keep it up during DDoS attacks (or if you're slashdotted ;)
This has gotta be one the easiest ways to boost the performance of your system.
The best place to look for reasons as to why this helps out so much is the FreeBSD Handbook: 9.2 Why Build a Custom Kernel?
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*This is the cute bunny virus, please copy this into your sig so it can spread
I wish there were more usefull step by step how-to stuff on the web like this. Too often I look for how to do something and I have to figure it out in bits an pieces.
It difficult for the people in the land between complete noob, and guru. It's like I'm an advanced user that has to admin his own box. ]:3}>
Pretty Pictures!
Some of the procedures described in these so-called "papers" (they are really too short to merit the name) are in direct contravention of the FreeBSD Project's recommended and supported procedures.
The recommended way to build a kernel is with the 'make buildkernel' command, after a successful 'make buildworld'.
Optimization levels higher than plain -O (such as the -O2 and -O3 levels recommended by the article) are known to trigger bugs in some of the inline assembler code in the FreeBSD kernel. In previous FreeBSD versions (that shipped with older gcc versions), they were also known to trigger compiler bugs.
The TOP_TABLE_SIZE option is irrelevant to system performance. Likewise, the NFS_NOSERVER option, although it reduces the size of the kernel, does not affect performance. Conversely, none of the truly important kernel options are explained or even mentioned.
The author mentions kern.ipc.maxsockets and kern.ipc.nmbclusters, but fails to mention kern.ipc.nmbufs which must be tuned to match kern.ipc.nmbclusters (the rule of thumb is one cluster for every other mbuf). Also, the suggested values (2048) are very low - lower than the default (which is computed at boot time as a function of physical memory size) and much lower than what a busy network server will need.
Admins who are truly concerned with the performance of their FreeBSD systems are advised to read the tuning(7) manual page, as well as some of the excellent FreeBSD books available from e.g. O'Reilly.
The papers are great but I'm missing a important aspect of it.
I don't know what kind of performance gains I can expect. It might not be worth the trouble if you gain a few percentage points compared to an unoptimized system. For me if an optimization can make you gain a 10% extra performance (or more!) it begins to be interesting.
The handbook mentions three reasons to compile your own kernel. None of them really makes much difference to performance:
Faster booting: yes, but that's not really performance in the sense being considered.
Saving memory: yes, but it'll only be a megabyte or two. Insignificant on most machines where performance is important.
Hardware support: yes, but that's not performance improvement.
So build your own kernel - it's educational if nothing else - but don't expect anything to run faster as a result. The only reason I build my own kernel is to apply some useful patches: one to spin down ATA disks when they're idle, and one to enable power-saving in the VIA chipset when the machine is idle (makes it *much* cooler).
Pre-5.2 RELEASEs ship with uniprocessor kernels. If you want SMP support, you have to recompile.
5.2, and future RELEASEs, will ship with SMP kernels. Due to the added overhead of kernel locking, this cuts kernel performance by about 20%. If you've got a uniprocessor machine, and you're doing kernel-intensive work, youll probably want to recompile.
Tarsnap: Online backups for the truly paranoid
Young fillys have no objection to someone playing with their pussy's. I have walked up on a pen full of strange fillys at night and they came right up to me and I petted them and felt up their pussys and they just lifted their tales and seemed to enjoy it.
Wild mares or those that have been artificially inseminated are usually reluctant to have sex. The wild ones are used to violent horsecock and the others have had peoples arms in their cunts so they can be apprehensive about sexual events.
Well, that depends on on what you're currently doing with your system. For example on one system which is pretty old (a P233), applying the recompiling performance optimizations let X run much faster. I think they'd be less obvious on a faster box. It really depensd on what bottlenext you're currently hitting.
Both articles give nice ideas, but it may not be a good idea to blindly follow their advices.
For instance, polling doesn't always improve things. Past the theory, I tried to enable device polling on a web server running FreeBSD 4.9-STABLE and the performance significantly _decreased_.
Also one of those papers suggests playing with extra GCC optimization flags. Well. First, don't expect your system to get significant speed improvements except for some very specific applications (usually not servers, rather intensive maths work).
Next, FreeBSD is not Gentoo Linux.
Gentoo has tons of users heavily testing all possible GCC optimization and discovering breakages. Those breakages are solved by adding extra patches, by backporting patches from CVS trees or by filtering annoying gcc flags for some piece of software. The whole thing works and it is even reliable because Gentoo Linux was designed that way and people use it that way.
On the other hand, almost no FreeBSD user use special flags. Even nothing but "-O" is explicitely recommended. There is no Gentoo-like workarounds for specific optimization flags. Nothing is really tested with extreme compiler optimization flags. So if you start playing with this, you may hit strange bugs and not a lot of people would have encoutered the same bug. So you're on your own. Your system may be unstable while your actual gain of performance will be near zero (really in a real world, bottlenecks are often disk/io, ram and network latency).
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FreeBSD committers are a bunch of *bleep*
Wow! After reading your kind words I just can't wait to try Gentoo. I want to be your friend and run the same code as you since you are so kind and friendly.
anyone who says that never walked into an isp. they must run one linux box at home, with a windoze machine for games. serious comuting there.
i wish anyone who said fbsd was dead/dying just fucking try it for a month. then they would change their mind.
In the DEVICE_POLLING part of the article, he says setting HZ=1000 in the kernel config slows town the clock, but that's wrong... it speeds it up... it ticks ever 1 ms instead of FreeBSD's default ever 10 ms. Last I checked that was speeding up not slowing down.