Ben Peart <peartben@xxxxxxxxx> writes: > Base Ref: master > Web-Diff: https://github.com/benpeart/git/commit/a0300882d4 > Checkout: git fetch https://github.com/benpeart/git read-index-multithread-v6 && git checkout a0300882d4 > > > This iteration brings back the Index Entry Offset Table (IEOT) extension > which enables us to multi-thread the cache entry parsing without having > the primary thread have to scan all the entries first. In cases where the > cache entry parsing is the most expensive part, this yields some additional > savings. Nice. > Test w/100,000 files Baseline Optimize V4 Extensions Entries > ---------------------------------------------------------------------------- > 0002.1: read_cache 22.36 18.74 -16.2% 18.64 -16.6% 12.63 -43.5% > > Test w/1,000,000 files Baseline Optimize V4 Extensions Entries > ----------------------------------------------------------------------------- > 0002.1: read_cache 304.40 270.70 -11.1% 195.50 -35.8% 204.82 -32.7% > > Note that on the 1,000,000 files case, multi-threading the cache entry parsing > does not yield a performance win. This is because the cost to parse the > index extensions in this repo, far outweigh the cost of loading the cache > entries. > ... > The high cost of parsing the index extensions is driven by the cache tree > and the untracked cache extensions. As this is currently the longest pole, > any reduction in this time will reduce the overall index load times so is > worth further investigation in another patch series. Interesting. > One option would be to load each extension on a separate thread but I > believe that is overkill for the vast majority of repos. Instead, some > optimization of the loading code for these two extensions is probably worth > looking into as a quick examination shows that the bulk of the time for both > of them is spent in xcalloc(). Thanks. Looking forward to block some quality time off to read this through, but from the cursory look (read: diff between the previous round), this looks quite promising.
