Linux on top of the OSF Mach3 Microkernel Linux on top of the OSF Mach3 Microkernel Linux on top of OSF MK The Mach3.0 Microkernel: Design • microkernel abstractions François Barbou des Places ([email protected]) • task, thread, port, message, memory object Nick Stephen ([email protected]) • resources and services represented as ports OSF Research Institute - Grenoble • interfaces implemented via RPC to an object port Task Message • Objectives: • widen the audience for the free OSF micro-kernel Ports • provide a complete and free platform to develop new Threads servers, applications or kernel extensions • provide Apple with a freely redistributable microkernel-based operating system for the Memory Apple/PowerMac platform Object Freely Redistributable Software Conference - 5 Feb 1996 - Cambridge 1/17 Freely Redistributable Software Conference - 5 Feb 1996 - Cambridge 2/17 Linux on top of the OSF Mach3 Microkernel Linux on top of the OSF Mach3 Microkernel The Mach3.0 microkernel: Benefits OSF MK Improvements • portability (modular design) • performance • symmetric multi-processing support • kernel-loaded servers (collocation) • thread migration • scalability (from desktop PCs to high-end multi-computers) • short-circuited RPC • extensibility • real-time • OS-neutrality • preemptable kernel • support for OS personalities running as user tasks • real-time RPC, priority inheritance • pageable, preemptable • distributed system (clusters and multi-computers) • more portable: isolated from hardware • DIPC: transparent Distributed IPC • simpler: no device drivers, scheduling, VM... • XMM: transparent distributed shared memory • external memory managers • more: MK++, CORDS (xkernel), Fault Tolerance, ... Freely Redistributable Software Conference - 5 Feb 1996 - Cambridge 3/17 Freely Redistributable Software Conference - 5 Feb 1996 - Cambridge 4/17 Linux on top of the OSF Mach3 Microkernel Linux on top of the OSF Mach3 Microkernel OSF MK on the Apple/PowerMac Linux Server • portability: no changes to machine-independent code Why Linux ? • validated with the MPTS (MK performance test suite) • pleasant and efficient development platform • initial target: PPC601 (PowerMac 7100 and 8100) • evolving very quickly: leverage the effort • support from Apple Computer, Inc. • heavily supported by Internet community • status • not derived from BSD • supports the Linux server • performant dynamic buffer cache • console, SCSI disk, serial port, ethernet drivers • X-Window running Drawbacks • next steps • portability: still quite biased towards PC • support more hardware (drivers, PPC603 and 604, • fast moving target PCI and CHRP PowerMacs) Freely Redistributable Software Conference - 5 Feb 1996 - Cambridge 5/17 Freely Redistributable Software Conference - 5 Feb 1996 - Cambridge 6/17 Linux on top of the OSF Mach3 Microkernel Linux on top of the OSF Mach3 Microkernel Linux Server: Design Constraints Linux Server: Code Reuse • leverage Linux evolution linux-1.2.13 + server • minimize changes to Linux code 1117 files • binary compatibility new server files Linux files • integration into the Linux tree: 188 929 • new “architectures”: osfmach3_i386 and osfmach3_ppc • machine-independent code in osfmach3 subdirectory machine new unmodified dependent PPC 866 • build on Linux or the Linux server 100 20 • serialized multi-threaded single server machine modified independent for server • no emulation library 88 43 • objective: performance parity with Linux ~ 50% of those files are in machine-dependent locations, but don’t really need to be ported Freely Redistributable Software Conference - 5 Feb 1996 - Cambridge 7/17 Freely Redistributable Software Conference - 5 Feb 1996 - Cambridge 8/17 Linux on top of the OSF Mach3 Microkernel Linux on top of the OSF Mach3 Microkernel Linux Server: Syscall Redirection Linux Server: Device Access emulation library syscall exception Linux Linux server sys_read sys_read emulation shared library memory block_read block_read ll_rw_block ll_rw_block OS user OS make_request make_request task device_reply_thread server server device intr user driver queue wait_on_buffer block_read_reply task copy data wait_on_buffer ... unlock_buffer ... end_request return ... unlock_buffer microkernel microkernel return microkernel - unprotected privileged code + safety device interfaces - complexity + unique and simple interface this code is common to all this code is replicated in - multi-threaded tasks - no optimized local syscalls block devices and machine each block device driver independent + optimized local syscalls Freely Redistributable Software Conference - 5 Feb 1996 - Cambridge 9/17 Freely Redistributable Software Conference - 5 Feb 1996 - Cambridge 10/17 Linux on top of the OSF Mach3 Microkernel Linux on top of the OSF Mach3 Microkernel Linux Server: Memory Management Linux Server: Signals and Time Linux Linux Server Fake Interrupts vm areas vm areas • signals normally processed on returned from interrupt or system call page tables dummy page tables • force signal delivery on user-mode-bound processes • take control of process by suspending and aborting microkernel Hardware MMU the Mach user thread if not in a system call VM interfaces • fall back to the exception handling path • Linux’s vm_area structs translated into Mach VM mappings Jiffies • keep dummy and generic page table code for code re-use • jiffies thread • mapped files • use Mach clock services to sleep 10 millisecs • memory object associated to an inode • call do_timer • inode pager (EMM) thread, serving requests from MK • simple but inefficient, will be redesigned Freely Redistributable Software Conference - 5 Feb 1996 - Cambridge 11/17 Freely Redistributable Software Conference - 5 Feb 1996 - Cambridge 12/17 Linux on top of the OSF Mach3 Microkernel Linux on top of the OSF Mach3 Microkernel Linux Server: Dynamic Buffer Cache Linux on OSF MK: Status on i*86 • cooperation between VM (microkernel) and Buffer Cache • boots from LILO (Linux server) • 100% binary compatible • emulate the free_area pool of pages in a memory object • supports virtual consoles, X-Window, gpm and sdoom ! • external memory manager: a Linux server thread • advisory pageout to avoid races and select page to free • current overall performance: 93% of Linux’s performance • memory_object_discard_request EMM interface • disk IO performance better than Linux • try_to_free_page() • memory_object_lock_request: let the MK release the page • biggest performance penalty on syscall path and copyin/out operations • MK falls back to default pager in case of problem • also avoids double paging (paging buffer cache pages) Freely Redistributable Software Conference - 5 Feb 1996 - Cambridge 13/17 Freely Redistributable Software Conference - 5 Feb 1996 - Cambridge 14/17 Linux on top of the OSF Mach3 Microkernel Linux on top of the OSF Mach3 Microkernel Linux on OSF MK: Conclusion Linux on OSF MK: Apple PowerMac Achievements • runs the available Linux/PPC commands and X-Window • OSF MK can support Linux and with good performance Further Information • a free development platform for OSF MK now exists Next Steps http://www.mklinux.apple.com • complete functionality and improve performance Availability • integrate Linux device drivers • summer 1996 • take advantage of OSF MK added value BOF Session at the OSF • multi-threaded tasks, SMP, real-time, clusters Snapshot Available for i*86 • this evening (Sunday Feb 5) from 8:30 to 10:00 PM • at OSF, 11 Cambridge Center - 100 yards from the Marriott http://www.gr.osf.org/mklinux • demo of Linux on OSF MK on Intel and PowerMac Freely Redistributable Software Conference - 5 Feb 1996 - Cambridge 15/17 Freely Redistributable Software Conference - 5 Feb 1996 - Cambridge 16/17 Linux on top of the OSF Mach3 Microkernel Linux on OSF MK: Apple PowerMac • runs the available Linux/PPC commands and X-Window Further Information http://www.mklinux.apple.com Availability • summer 1996 BOF Session at the OSF • this evening (Sunday Feb 5) from 8:30 to 10:00 PM • demo of Linux on OSF MK on Intel and PowerMac Freely Redistributable Software Conference - 5 Feb 1996 - Cambridge 17/17.