Am 10.10.2013 22:19, schrieb Sebastian Schuberth: > Please keep in mind to CC the msysgit mailing list for Windows-specific > stuff. I'm also CC'ing Karsten who has worked on performance improvements for > Git for Windows in the past. >
Thanks > Thanks for bringing this up! > > -- > Sebastian Schuberth > > >> Hi folks, >> >> I don't follow the mailing list carefully, so forgive me if this has >> been discussed before, but: >> >> I've noticed that when working with a very large repository using msys >> git, the initial checkout of a cloned repository is excruciatingly >> slow (80%+ of total clone time). The root cause, I think, is that git >> does all the file access serially, and that's really slow on Windows. >> What exactly do you mean by "excruciatingly slow"? I just ran a few tests with a big repo (WebKit, ~2GB, ~200k files). A full checkout with git 1.8.4 on my SSD took 52s on Linux and 81s on Windows. Xcopy /s took ~4 minutes (so xcopy is much slower than git). On a 'real' HD (WD Caviar Green) the Windows checkout took ~9 minutes. That's not so bad I think, considering that we read from pack files and write both files and directory structures, so there's a lot of disk seeking involved. If your numbers are much slower, check for overeager virus scanners and probably the infamous "User Account Control" (On Vista/7 (8?), the luafv.sys driver slows down things on the system drive even with UAC turned off in control panel. The driver can be disabled with "sc config luafv start= disabled" + reboot. Reenable with "sc config luafv start= auto"). >> Has anyone considered threading file access to speed this up? In >> particular, I've got my eye on this loop in unpack-trees.c: >> Its probably worth a try, however, in my experience, doing disk IO in parallel tends to slow things down due to more disk seeks. I'd rather try to minimize seeks, e.g.: * read the blob data for a block of cache_entries, then write out the files, repeat (this would require lots of memory, though) * index->cache is typically sorted by name and pack files by size, right? Perhaps its faster to iterate cache_entries by size so that we read the pack file sequentially (but then we'd write files/directories in random order...) If you want to measure exactly which part of checkout eats the performance, check out this: https://github.com/kblees/git/commits/kb/performance-tracing-v3 Bye, Karsten -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
