On Sat, Oct 28, 2000 at 09:14:18AM +0900, OKUJI Yoshinori wrote: > From: Ron Farrer <[EMAIL PROTECTED]> > Subject: Re: [Hurd-alpha-devel] Re: L4 instead of gnumach? > Date: Fri, 27 Oct 2000 16:19:30 -0700 > > > This is not completely decided. A MACH emulation layer for L4 was the > > original idea, but I'm completely open to other suggestions. > > To understand why Mach emulation is bad, you need to know how L4 > improved IPC performance. They have improved the performance in > various aspects, but in simple words, they made IPC semantics more > lean.
Sure: IPC mesages need to be aligned on page boundaries (as the message passing actually is page passing inside the MMU), there is a limit of 128 threads in a task and so on. > If you add the extra flesh again, the performance would be the > same as Mach. In fact, they demonstrated this in the paper on > Unix/L3. Anyway, read articles/papers on L3/L4 as many as > possible. You should be able to realize how difficult getting good > perfomance is. Very careful optimizations are necessary (e.g. see the > paper on L4-Linux). > > However, I think Mach emulation would be a good thing as the first > step, because you will be able to investigate how different L4 is from > Mach and what would be necessary to be done in details. But I'd like > to point out that Mach emulation should be temporary but not a > permanent solution. Indeed. The nice thing about L4 is that it's simple and lean, and therefore fast. The emulation layer will definitely reduce speed. For example with IPC: I think the way to emulate the Mach behaviour (and to circumvent the page alignment) is to copy contents into page aligned memory blocks. But I think speed improvements can be done later on, especially because it will need *careful* optimizations. > > MACH uses cthreads, we figured it would keep things easier by going that > > route. If you think otherwise I'd like to know why? > > Isn't your (ultimate) goal to remove Mach-things from Hurd? cthreads > is a Mach-only multithreading method, while pthreads is designed for a > platform-independent manner. In addition, obviously, much more > programmers know pthreads than cthreads. Um, how quickly will HURD/the HURD people switch to pthreads? I mean, we want to run HURD on top of it, and HURD uses cthreads at the moment. > > Overall we want to give HURD some type of direction to go and some type > > of common goal for development. > > That's a very, very good thing. It is certain that big projects such > as Hurd cannot be cooperatively developed without clear goals. I'm > quite glad to hear that you make an effort. Please call me out when > you begin the work. I'd like to participate. :) We will have questions about drivers, and you did add Linux drivers to GNUMach, no? > (Of course, I won't devote myself to L4 until I finish the remaining > tasks for GRUB 1.0, though...) Now you talk about Grub.... :-) Alpha still needs a multiboot loader (well, I can't find one). L4 is loaded as raw image on Alpha at the moment. I don't know if you have access to an Alpha, but it would be very nice to have a bootloader (for example aboot) modified so it can load multiboot stuff. Erik Verbruggen.
