copyright20xxsonycorporation(參考版)
2025-07-18 18:14本頁(yè)面
【正文】 t know if this is possible ? Need to find parts of heap that are identical on each boot ? Probably need separate alwaysthesame and maychange classes ? Need careful analysis, and might need knowledge of each class Optimize Package Scan ? Most definitely! This should be first thing attacked ? I tried first order optimization ? Removed perfile signature check in parseZipArchive() ? This reduced duration of this routine (cumulative for 138 calls) by several seconds ? But… total boot time was not reduced (!!) ? Toothpaste effect strikes again! ? Need to continue analysis ? May need to switch to a pressed flash file system, instead of managing indexing and pression in user space. Miscellaneous ? zoneinfo inefficiences ? Discovered with strace ? Routine that does read syscall for 40 bytes, then 8 bytes, then another 8 bytes (hundreds of times) ? No buffering at user level ? Sloppy loop coding ? Linear scan of timezone file ? For a file not present!! ? Probably only a few hundred milliseconds, but worth changing readahead ? I got interesting results from prefilling the page cache ? Just added following to / ? Results: ? Use of cat delayed start of class preloading by ~2 seconds ? Reduces package scan time by ~10 seconds ? Reduced total boot time by ~5 seconds service preload /system/bin/cat /system/framework/ /system/app/ /system/app/ /system/app/ /system/app/ /system/app/ /system/app/ /data/app/ /dev/null oneshot Readahead notes ? Could use [s|u]readahead to prefill page cache ? Note: Bionic is missing readahead syscall definition and libc call ? However… ? Using readahead masks bad behavior ? (half of ) is read 4 times! during boot ? Filling page cache makes reads after first one fast, but it would be better to avoid (most of) the reads altogether ? Would be good to just optimize or eliminate parseZipArchive() ? sreadahead should be used as last optimization (after all other enhancements) Conclusions ? Only about 5 seconds reduction in boot time ? From prefilling page cache with ?cat? ? Warning: On dev board with NFS rootfs ? But, have a good foundation and set of tools for improving things going forward ? Good idea of where time is spent Observations ? “Premature optimization is the root of all evil” ? Be very careful of optimizing wasteful operations ? Better to improve or eliminate the operations, than hide the wasteful operations with caching ? Beware of systemic or architectural problems ? Package management basically builds a persistent container and pression architecture in user space ? Except, it does it poorly. (It rebuilds the inmemory data structure for indexing an archive over and over.) ? Just use a file system, for heaven39。t be read later ? . Entire package file is read, when only the file is requested Ideas for Improvements ? First, a side note on toothpaste.. ? Kernel
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