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NetBSD Now Has Native pthreads!
jschauma writes, quoting the NetBSD changelog, was one of several people to point out that "Jason Thorpe has merged the nathanw_sa branch with -current. NetBSD
now has a high performance, modern kernel thread implementation using
Scheduler
Activations in the main source tree. This work was performed by
Nathan Williams with contributions by several other developers."
Many NetBSD ports already have SMP support - SA is somewhat related, but mostly it a completely different thing.
The Alpha and VAX ports have had SMP for a long time, i386 was added a couple of months ago, and Sparc was just recently incorported into the -current tree. PowerPC Macs also have SMP support, and maybe some other ports I don't recall at the moment.
Now when I run configure I won't have to wonder why :)
it can never figure out why I don't have any type of threading
in my system. NetBSD Rulz!
NetBSD has had SMP support for a few platforms in the -CURRENT branch for a while now (sparc, vax and alpha for sure).
Even with SMP support, I don't think you get a really high degree of concurrency unless you have a threading implementation that involves the kernel.
FreeBSD 4.x on a dual processor machine, for example, will take each process currently running, and assign it to a free CPU (either 0 or 1). This works great if you have more than one process running on your machine with a good division of labour (i.e. Apache + MySql).
However, there are times when you want your box to be dedicated to a single purpose like being a datbase server only. That database engine might be a single process application like Oracle, and was written to break it's own internal tasks off into threads.
A kernel thread implementation means you don't waste the second CPU of your SMP capable OS in this situation.
Way to go NetBSD team, for implementing this. I hope I get to see this in action in 1.7
Success is as dangerous as failure, hope as hollow as fear.
Glad to see NetBSD is keeping up with the rest of the world.
While (native)threading support has taken quite some time to come to NetBSD one
can be assured that the implementation is done right, as always with NetBSD.
SMP means running processes on more than one CPU in parallel. (With some care-taking from the kernel that both CPUs don't step on each other WRT writing to kernel data structures etc.).
:) threads, and let them run on either one or more than one CPU. This is basically an application-layer thing, in contrast to SMP which happens inside the kernel. Of course having SMP available helps for performance in threads systems as you can run threads in parallel on several CPUs, but SMP is not strictly necessary for a threaded system.
Threading means splitting up a process into several (well
Many applications today use a threaded software architecture (over the classical Unix "fork"ed processes), and so having some efficient threads implementation is very important.
With the Scheduler Activations based work that Jason and Nathan made, this is a very efficient implementation as you can map N userland threads to M kernel threads, and you don't have one kernel thread for each userland thread, like some other systems (used to?) have, and which kills performance if you have many threads.
- Hubert
All that's true, but when you have a multithreaded process, there's an efficiency loss if two threads from the same process are running on different CPUs. Since threads from the same process tend to access the same memory addresses, you don't get the normal advantages of CPU memory caching.
Scheduler Activations are nice, and sort of classic for BSD systems too. I wonder how they compare with FreeBSD's KSE.