Sujit Karataparambil wrote: > Is it disabled in the proprietary operating system. It is an misnomer > that MMU Slows down the embedded application. > Certainly debatable. > > The key issue is do you have enough memory to turn on the MMU. Say an > 4K Memory to 256M Memory the requirements are > different. > > When you say that the CPU has MMU, It would be wise to add memory to > the device and turn on MMU.
I'd say the opposite. Often having an MMU uses _less_ memory. Part of the saving comes from easier shared libraries, demand paging, and copy-on-write fork. Part of the saving comes from greatly reduced memory fragmentation. Without an MMU fragmentation is often a problem, and can mean you need to keep 30% extra memory "free" just to be able to allocate what you need. The exact requirement depends a lot on the application. For speed, even if the CPU runs slower with an MMU, there are many speed advantages from it. Again there's copy-on-write fork. Also, the kernel is able to cache more filesystem data and things like that. OVerall if you think there MMU might have a performance penalty and you can switch it on/off - why not just try both, and see which is easier to use and which performance better for real applications doing stuff? If you have FDPIC ELF support on your architecture, FDPIC ELF executables can be run on kernels with and without MMU, so you can try the same userspace on different kernels and compare performance and memory behaviour. -- Jamie _______________________________________________ uClinux-dev mailing list [email protected] http://mailman.uclinux.org/mailman/listinfo/uclinux-dev This message was resent by [email protected] To unsubscribe see: http://mailman.uclinux.org/mailman/options/uclinux-dev
