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string-list: use ALLOC_GROW macro when reallocing string_list

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Use ALLOC_GROW() macro when reallocing a string_list array
rather than simply increasing it by 32.  This is a performance
optimization.

During status on a very large repo and there are many changes,
a significant percentage of the total run time is spent
reallocing the wt_status.changes array.

This change decreases the time in wt_status_collect_changes_worktree()
from 125 seconds to 45 seconds on my very large repository.

This produced a modest gain on my 1M file artificial repo, but
broke even on linux.git.

Test                                            HEAD^^            HEAD
---------------------------------------------------------------------------------------
0005.2: read-tree status br_ballast (1000001)   8.29(5.62+2.62)   8.22(5.57+2.63) -0.8%

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jeff Hostetler 2017-04-14 19:51:52 +00:00 committed by Junio C Hamano
parent 3b9e3c2ced
commit 950a234cbd
2 changed files with 50 additions and 4 deletions
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5
string-list.c
View File

@ -41,10 +41,7 @@ static int add_entry(int insert_at, struct string_list *list, const char *string
if (exact_match)
return -1 - index;
if (list->nr + 1 >= list->alloc) {
list->alloc += 32;
REALLOC_ARRAY(list->items, list->alloc);
}
ALLOC_GROW(list->items, list->nr+1, list->alloc);
if (index < list->nr)
memmove(list->items + index + 1, list->items + index,
(list->nr - index)

49
t/perf/p0005-status.sh Executable file
View File

@ -0,0 +1,49 @@
#!/bin/sh
#
# This test measures the performance of various read-tree
# and status operations. It is primarily interested in
# the algorithmic costs of index operations and recursive
# tree traversal -- and NOT disk I/O on thousands of files.
test_description="Tests performance of read-tree"
. ./perf-lib.sh
test_perf_default_repo
# If the test repo was generated by ./repos/many-files.sh
# then we know something about the data shape and branches,
# so we can isolate testing to the ballast-related commits
# and setup sparse-checkout so we don't have to populate
# the ballast files and directories.
#
# Otherwise, we make some general assumptions about the
# repo and consider the entire history of the current
# branch to be the ballast.
test_expect_success "setup repo" '
if git rev-parse --verify refs/heads/p0006-ballast^{commit}
then
echo Assuming synthetic repo from many-files.sh
git branch br_base master
git branch br_ballast p0006-ballast
git config --local core.sparsecheckout 1
cat >.git/info/sparse-checkout <<-EOF
/*
!ballast/*
EOF
else
echo Assuming non-synthetic repo...
git branch br_base $(git rev-list HEAD | tail -n 1)
git branch br_ballast HEAD
fi &&
git checkout -q br_ballast &&
nr_files=$(git ls-files | wc -l)
'
test_perf "read-tree status br_ballast ($nr_files)" '
git read-tree HEAD &&
git status
'
test_done