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Measured Performance of Commodity Operating Systems

This presentation provides the initial remarks and findings of a study conducted at Harvard University on the performance of different commodity operating systems. The study evaluates various aspects such as CPU mode changes, instruction counts, cache and TLB misses, graphics performance, network throughput, and application workloads. The results highlight the strengths and weaknesses of each operating system, with Windows NT showing higher instruction counts and cache misses compared to NetBSD and Windows.

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Measured Performance of Commodity Operating Systems

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  1. Measured Performance of Commodity Operating Systems Work done at Harvard University CSE-597A Presentation V.N.Murali

  2. Initial Remarks • Any ideas? • Windows for Workgroups:Most expensive due to frequent changes in machine mode and system call hooks. • NT:more efficient than above,overhead due to microkernel-like design(Win-32 API is a user-level server) • NetBSD:Most efficient

  3. Components

  4. Device Drivers • Windows::VxD(virtual Device Drivers) which are activated by hardware interrupts,system calls and/or entry points. • NetBSD::/dev file is installed.Load a driver and access the counter using the device file.Configured using ioctl() • NT::DDk is the API for driver development.Loaded into the NT executive

  5. Microbenchmarks • Null :: counter access latency. • Syscall :: minimum system call latency • Exec :: latency to load and run a program • Memory access time :: access times for arrays (various sizes) • File System • BitBlt :: Graphics subsystems • Network

  6. Application workloads • Wish :: command interpreter for the Tcl language (test for GUI subsystem,CPU intensive,very little Disk activity) • Ghostscript • WWW server • (ASSUMPTIONS:Single user mode,little or no background activity)

  7. Metrics • Cycle counts. • Instruction counts ? ( Would this be a correct metric ?) • Data read/write references ??(Similar arguments) • Cache and TLB misses (Icache,Dcache,ITLB,DTLB)

  8. RESULTSNull micro • Least instruction count : Windows. Why? • Maximum instruction count: Windows NT.Why? • Higher CPI : Windows.Why? • Highest cycle counts : NT.Why? • Highest instruction cache miss : NT.Why?

  9. RESULTSSyscall micro • Used a simple system call(dup) on UNIX and NT.Get_extended_error_info (16bitWin,int21),get_interrupt_vector (32bit,int 21).. • Overhead for dup in NT and BSD is same as Null benchmark.Similar behavior in I-cache misses for NT. • Most efficient in terms of cycle counts? Windows 32 bit system call?

  10. Contd. • Windows 16 bit is very expensive?Why? • Hooks?System calls can be intercepted in DOS.Used for CDROM drivers,caching etc • Most Efficient:NetBSD and Windows 32 bit.Both NT and Windows 16 are expensive.

  11. RESULTSExec micro • NetBSD uses a vfork() and exec() combo while NT uses CreateProcess().Windows has a shared address space,so nothing is created. • Most efficient : NetBSD static.Why? • Worst :NT dynamic.Why?

  12. Contd.. • Windows overhead is higher than NetBSD static and lower than either OS’s dynamic linkage • Maximum data reads and writes : NT.Why? • Dynamic linkage incurs a lot of overhead.

  13. RESULTSMemory Access time • Repeated references to arrays of various sizes using stride=128bytes. • 8k on chip cache and 256K onboard cache. • NT uses a deterministic page mapping policy => similar performance upto 256K and smooth degradation afterwards • NetBSD uses a non-determinstic page mapping policy.Hence poor performance for >8k size

  14. Contd. • NT’s file system buffer cache is integrated to the VM system.This rings a bell doesn’t it?? • 64k segment size in Windows limits performance

  15. RESULTSFile System Micro • 3 activities,a)Hit in disk cache b)Access to small files c)Creation • Tested NTFS and FAT32 for Windows NT,FAT 16,32 for Windows,FFS for NetBSD. • Least overhead: NetBSD • Most overhead : NT/NTFS,FAT 16.

  16. Contd.. • Meta data updates :NTFS performs the best because it logs them,while FFS performs poorly because of synchronous writes.

  17. RESULTSGraphics micro • Display an array of pixels repeatedly • Worst performance . NetBSD.Why? • NETWORK THROUGHPUT • Worse code locality for NT => instruction cache and TLB misses. • However throughput is comparable to BSD.Limitation is due to the ethernet.

  18. Summary • Frequent CPU mode changes in Windows : expensive • 64K segment size is a limitation • Higher instruction counts and cache misses for NT ?Why? • Efficient graphics and relaxed file system semantics in NT

  19. Application workloads • Wish:Overhead includes context switches and IPC.Highest overhead in Windows.Why? • NT is worse than BSD.Why? • Ghostscript: Best performance by NT and Windows • Web Server:Best results for NetBSD and Windows,Worst results for NT.NT is believed to have a very poor network implementation.

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