L4/Darwin: Evolving UNIX. Charles Gray Research Engineer, National ICT Australia

Transcription

1 L4/Darwin: Evolving UNIX Charles Gray Research Engineer, National ICT Australia

2 Outline 1. Project Overview 2. BSD on the Mach microkernel 3. Porting Darwin to the L4 microkernel 4. Project Status 2

3 Darbat Overview Para-virtualised Darwin kernel L4 μ-kernel hypervisor Isolated kernel and device drivers Standard virtualisation benefits 3

4 Why? Virtualisation Flexibility Robustness Code size 4

5 Linux Size (LoC) 7,000,000 6,000,000 5,000,000 4,000,000 3,000,000 2,000,000 1,000,

6 Mach Once a hot research topic Application Application Many attempts at BSD on Mach Darwin is a monolithic Mach kernel Gave microkernels a bad name Process Mgr Disk File System Network Mach 6

7 What s in a kernel? XML parser Decompression algorithms Linker Network routing Device drivers Strings 7

8 Mac OS X Architecture Darwin OS X App launchd UNIX App Aqua GUI xnu 8

9 Darwin UNIX App OS X App BSD Mach I/O Kit Unique kernel design Mach 3.0 μ-kernel 4.4 BSD derivative I/O Kit device drivers Mac OS X applications Full FreeBSD 5 UNIX environment 9

10 BSD Layer BSD fork() mmap() listen() HFS+ TCP UFS Threads Process UBC Scheduler VM Disk Network Mach PCI Bus I/O Kit interrupt 10

11 The I/O Kit mach_msg() BSD paging HFS+ Partition0 Partition1 Client Disk0 Disk1 Keyboard ATA NIC UHCI interrupt Mach PCI Bus I/O Kit 11

12 BSD and I/O Kit BSD HFS+ read() ioctl() bdevsw Partition0 Partition1 Disk0 Disk1 SCSI ATA I/O Kit 12

13 L4 2nd generation u-kernel Learn from mistakes of Mach Pay attention to cache, TLB, complexity Make microkernels work 10-20x performance improvement over Mach 13

14 L4 μ-kernel OS Application Application IPC Threads Address Spaces Scheduler interrupt page-fault / exception L4 14 not to scale

15 Darbat Decompose Darwin kernel Tackle complexity problem Add flexibility Maintain (or improve) performance All with binary compatibility 15

16 Darbat Model UNIX App OS X App BSD BSD Mach Mach timer Drv. Stub Drv. Stub L4 BSD stub BSD stub I/O Kit I/O Kit xnuglue xnuglue interrupt 16

17 XNU on L4 page faults syscalls timer int. mask exception I/O Kit ISR Thread Work-loop Thread Mach 17

18 Server Consolidation xnu xnu I/O Kit L4 Multiple OS instances support Simplified driver model 18

19 Crashable Drivers Drivers crash Holding locks Hogging resources Can isolate drivers and keep performance Some devices still critical xnu Network Disk Stack Stack L4 19

20 VM Aware Scheduling Application Application priority Application Application Application xnu xnu xnu L4 20

21 Reliable Servers xnu Key Mgr. Microkernel is very resilient I/O Kit Watchdog L4 Protect data from 3rd party modules Ensure reliable execution of code Cheaper software solutions 21

22 Heterogeneous Systems L4 is OS (everything?) agnostic Linux *BSD Share devices Share file systems Wombat Linux L4 xnu I/O Kit 22

23 System Call Performance Mac OS X Darbat 0.2 UNIX App ~2500 cycles UNIX App ~2400 cycles xnu xnu L4 mach_msg null operation 23

24 In-task Synchronisation Mac OS X UNIX App Darbat UNIX App xnu ~17,000 cycles ~6,500 cycles L4 pthreads synchronisation 24

25 IPC Optimisation OS X App OS X App L4 IPC is a subset of Mach IPC Applications rely on Mach semantics Optimisation for some messages xnu L4 25

26 Scripting Sometimes you just need a hack In-kernel scripts get messy Scheduling and locks are a pain Don t compromise the whole system xnu Python I/O Kit L4 26

27 Lessons So Far Darwin modularity Binary compatibility Mac OS X has bugs Performance Debugging 27

28 Future Work? Further decomposition Improved xnu and I/O Kit bindings Usable system! Experiment with features System benchmarks 28

29 Summary UNIX kernels are feature-packed L4 is one option to address this problem Extend UNIX kernel to meet modern usage Questions? 29