On Mon, 2008-07-14 at 12:35 -0400, erik quanstrom wrote: > > > Plan 9 makes it easy via 9p, its file system/resource sharing > > > protocol. In plan 9, things like graphics and network drivers export a > > > 9p interface (a filetree). Furthermore, 9p is network transparent > > > which means accesses to remote resources look exactly like accesses to > > > local resources, and this is the main trick - processes do not care > > > whether the file they are interested in is being served by the kernel, > > > a userspace process, or a machine half way across the world. > > > > All very true. And it sure does provide enormous benefits on distributed > > memory architectures. But do you know of any part that would be > > beneficial for highly-SMP systems? > > do you have some reason to believe that 9p (or just read and write) > is not effective on such a machine?
I have some (not a whole lot, since I haven't looked at source code for a while) reason to believe that the current 9P implementation doesn't seem to exploit the opportunity when both ends happen to run on the same shared memory. I would love to be proved wrong. Although, the higher level issue that I have with 9P on a shared memory architectures is the fact that file and communication abstractions might not be the best way to represent the shared memory resources to begin with. IOW, mmap()-like things might be a closer match. > since scheduling would be the main shared resource, do you think > it would be the limiting factor? Yes. And that's where the comment in my first email came from: scheduling is a tricky thing on a shared memory NUMA-like systems. Solaris's scheduler is not shy when it comes to big iron (100+ CPU SMP boxes) but even it had to be heavily tuned when a Batoka box first came to the labs. When you have physcical threads (CPUs), virtual threads and a non trivial memory hierarchy -- the decision of what is the best place (hardware-wise) for a give thread to run becomes a non-trivial one. Kernels that can track affinity properly rule the day. I don't think that Plan9 scheduler has had an opportunity to be tuned for such an environment. Same goes for virtual memory page related algorithms. Here's a decent (albeit brief) overview of what kernel has to face these days in order to be reasonably savvy on shared memory, multicore architectures with NUMA-like memory hierarchy: http://www.redhat.com/promo/summit/2008/downloads/pdf/Wednesday_1015am_Rik_Van_Riel_Hot_Topics.pdf Start from slide #13. Thanks, Roman.
