summaryrefslogtreecommitdiff
path: root/t/helper/test-dump-untracked-cache.c
diff options
context:
space:
mode:
authorLibravatar Nguyễn Thái Ngọc Duy <pclouds@gmail.com>2018-08-18 16:41:24 +0200
committerLibravatar Junio C Hamano <gitster@pobox.com>2018-08-18 09:47:46 -0700
commitb4da37380b7774248086f42bcd59397a44e1ac79 (patch)
tree0d99705cb08e16671125a37bc2ee2f9574f1e487 /t/helper/test-dump-untracked-cache.c
parentunpack-trees: add performance tracing (diff)
downloadtgif-b4da37380b7774248086f42bcd59397a44e1ac79.tar.xz
unpack-trees: optimize walking same trees with cache-tree
In order to merge one or many trees with the index, unpack-trees code walks multiple trees in parallel with the index and performs n-way merge. If we find out at start of a directory that all trees are the same (by comparing OID) and cache-tree happens to be available for that directory as well, we could avoid walking the trees because we already know what these trees contain: it's flattened in what's called "the index". The upside is of course a lot less I/O since we can potentially skip lots of trees (think subtrees). We also save CPU because we don't have to inflate and apply the deltas. The downside is of course more fragile code since the logic in some functions are now duplicated elsewhere. "checkout -" with this patch on webkit.git (275k files): baseline new -------------------------------------------------------------------- 0.056651714 0.080394752 s: read cache .git/index 0.183101080 0.216010838 s: preload index 0.008584433 0.008534301 s: refresh index 0.633767589 0.251992198 s: traverse_trees 0.340265448 0.377031383 s: check_updates 0.381884638 0.372768105 s: cache_tree_update 1.401562947 1.045887251 s: unpack_trees 0.338687914 0.314983512 s: write index, changed mask = 2e 0.411927922 0.062572653 s: traverse_trees 0.000023335 0.000022544 s: check_updates 0.423697246 0.073795585 s: unpack_trees 0.423708360 0.073807557 s: diff-index 2.559524127 1.938191592 s: git command: git checkout - Another measurement from Ben's running "git checkout" with over 500k trees (on the whole series): baseline new ---------------------------------------------------------------------- 0.535510167 0.556558733 s: read cache .git/index 0.3057373 0.3147105 s: initialize name hash 0.0184082 0.023558433 s: preload index 0.086910967 0.089085967 s: refresh index 7.889590767 2.191554433 s: unpack trees 0.120760833 0.131941267 s: update worktree after a merge 2.2583504 2.572663167 s: repair cache-tree 0.8916137 0.959495233 s: write index, changed mask = 28 3.405199233 0.2710663 s: unpack trees 0.000999667 0.0021554 s: update worktree after a merge 3.4063306 0.273318333 s: diff-index 16.9524923 9.462943133 s: git command: git.exe checkout This command calls unpack_trees() twice, the first time on 2way merge and the second 1way merge. In both times, "unpack trees" time is reduced to one third. Overall time reduction is not that impressive of course because index operations take a big chunk. And there's that repair cache-tree line. PS. A note about cache-tree invalidation and the use of it in this code. We do invalidate cache-tree in _source_ index when we add new entries to the (temporary) "result" index. But we also use the cache-tree from source index in this optimization. Does this mean we end up having no cache-tree in the source index to activate this optimization? The answer is twisted: the order of finding a good cache-tree and invalidating it matters. In this case we check for a good cache-tree first in all_trees_same_as_cache_tree(), then we start to merge things and potentially invalidate that same cache-tree in the process. Since cache-tree invalidation happens after the optimization kicks in, we're still good. But we may lose that cache-tree at the very first call_unpack_fn() call in traverse_by_cache_tree(). Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 't/helper/test-dump-untracked-cache.c')
0 files changed, 0 insertions, 0 deletions