Hi Noah, sun4u supports multiple address space indicators (ASI). Each user process has one and the kernel has one. In kernel mode, it's possible to access the user address space through the secondary ASI. This means that both user and kernel address spaces can extend to the full 32-bit or 64-bit range (depending on the bitness and other architectural constaints) and marshalling data between user processes and the kernel is cheap.
On architectures without this concept (e.g. x86 and x64), either you need to bite off a chunk of the address space as a shared range that's reserved for the kernel or you have to incur expensive context switches every time you want to move data between a user process and the kernel (I think there's some crazy variant of Linux that does this). I'm not sure if PPC has something analagous to the secondary ASI, but I'm sure someone lurking on this list can fill us in. Adam On Mon, Oct 31, 2005 at 08:48:15PM -0800, Noah Yan wrote: > I just realized that for Solaris x86, userland and kernel share the same > address space (4G in 32bit), like the 3G/1G split in Linux and other kernel, > but in SPARC sun4u, the user and kernel have separate address space, each > with 4G in 32-bit. > > Is it just a matter of having different size of AS, or other reasons? > What is the advantage of the shared one over the separated one? > What is the advantage of the separated one over shared one? > Why solaris makes the difference for the x86 and SPARC? I mean what the > difference of the architecture cause this. > Also seems sun4d has shared AS, what cause Solaris use the separate AS in > sun4u? > For PowerPC implementation, which approach should we use, and why? > > So many questions:), Forgive for a newbie who is eager to learn and thanks in > advance. > > Noah > This message posted from opensolaris.org > _______________________________________________ > powerpc-discuss mailing list > powerpc-discuss at opensolaris.org -- Adam Leventhal, Solaris Kernel Development http://blogs.sun.com/ahl
