1 / 6

Patterson Consulting Radical Proposal: Let’s help real problems

Patterson Consulting Radical Proposal: Let’s help real problems. Dave Patterson University of California at Berkeley Patterson@cs.berkeley.edu April 2001. Execution. 2 Bus Intf. D cache. TLB. Out-Of-Order. branch. SS. Icache. What have designers been doing?.

eli
Download Presentation

Patterson Consulting Radical Proposal: Let’s help real problems

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Patterson Consulting Radical Proposal: Let’s help real problems Dave Patterson University of California at Berkeley Patterson@cs.berkeley.edu April 2001

  2. Execution 2 Bus Intf D cache TLB Out-Of-Order branch SS Icache What have designers been doing? • Performance, Performance, Performance; 2X/18 months • Superscalar, 3 levels of cache, branch prediciton, out-of-order execution, … • If performance right goal, then > 1GHz => sales jump • ~ Year 2000 v. 1999 car sales • What Happened? • US PC market shrank 3.5 % 1Q01; 1st shrink in 7 yrs! • Performance no longer hard? Pentium III

  3. Time to help on other problems? • Software quality? • Fry’s Law: 2X programming productivity every 18 years • Last architectural assist was virtual memory protection, 1970? • SW Engineering perspective on SW bugs: • Bugs reproducible from inputs will be repaired • Transient errors very hard to fix • Jim Gray hypothesis: • Most production software bugs are soft - Heisenbugs • Bohrbugs, like the Bohr atom, are solid, easily detected by standard techniques, and hence boring • Then can repair most SW bugs by restart

  4. What should HW designers do? • Already have heavyweight transactions in, databases, operating systems • atomic event that can be completely undone if fails midstream • Expensive so done only on some disk operations • Support lightweight transactions in CPU 1) Help with restart of routines to fix Heisenbugs 2) Make Software error recovery more reliable • Start transaction • SW detects error • back out all evidence of work to original place

  5. What will it take? • Mechanisms in modern CPUs for performance speculation lay foundation • Speculative execution via branch prediction, out-of-order execution, in-order completion allows “transactions” per branch, preserving interrupts: Reorder Buffer, Memory Buffer, Commit Table, … • Transmeta Crusoe provides • software control of Write Buffer, allowing SW to discard results of speculative SW execution; • shadowed registers so can go to old values • Expand these mechanisms to support transactions to help with SW bugs • Shadow registers, Much Bigger write buffer (100 KB?) under SW control

  6. Summary • Performance no longer the only problem • Last 15 years: Processors 1000X faster, memories 1000X bigger allow SW 1000X bigger • No help to SW in last 15 years • 1 bugs / 1000 lines of code, millions of lines of code • Real problem is SW • Like Simulateneous Multithreading, which uses existing OOO HW to improve throughput of threads, Tranaction support uses existing OOO HW and SW mechanisms to provide undo for SW bugs, SW repair • Solve an important problem, no performance!

More Related