rust: peek_mut optim for lazy ancestors
This is one of the two optimizations that are also
present in the Python code: replacing pairs of pop/push
on the BinaryHeap by single updates, hence having it
under the hood maintain its consistency (sift) only once.
On Mozilla central, the measured gain (see details below)
is around 7%.
Creating the PeekMut object by calling peek_mut() right away
instead of peek() first is less efficient (gain is only 4%, stats
not included).
Our interpretation is that its creation has a cost which is vasted
in the cases where it ends by droping the value (Peekmut::pop()
just does self.heap.pop() anyway). On the other hand, the immutable
peek() is very fast: it's just taking a reference in the
underlying vector.
The Python version still has another optimization:
if parent(current) == current-1, then the heap doesn't need
to maintain its consistency, since we already know that
it's bigger than all the others in the heap.
Rust's BinaryHeap doesn't allow us to mutate its biggest
element with no housekeeping, but we tried it anyway, with a
copy of the BinaryHeap implementation with a dedicaded added
method: it's not worth the technical debt in our opinion
(we measured only a further 1.6% improvement).
One possible explanation would be that the sift is really fast
anyway in that case, whereas it's not in the case of Python,
because it's at least partly done in slow Python code.
Still it's possible that replacing BinaryHeap by something more
dedicated to discrete ordered types could be faster.
Measurements on mozilla-central:
Three runs of 'hg perfancestors' on the parent changeset:
Moyenne des médianes: 0.100587
! wall 0.100062 comb 0.100000 user 0.100000 sys 0.000000 (best of 98)
! wall 0.135804 comb 0.130000 user 0.130000 sys 0.000000 (max of 98)
! wall 0.102864 comb 0.102755 user 0.099286 sys 0.003469 (avg of 98)
! wall 0.101486 comb 0.110000 user 0.110000 sys 0.000000 (median of 98)
! wall 0.096804 comb 0.090000 user 0.090000 sys 0.000000 (best of 100)
! wall 0.132235 comb 0.130000 user 0.120000 sys 0.010000 (max of 100)
! wall 0.100258 comb 0.100300 user 0.096000 sys 0.004300 (avg of 100)
! wall 0.098384 comb 0.100000 user 0.100000 sys 0.000000 (median of 100)
! wall 0.099925 comb 0.100000 user 0.100000 sys 0.000000 (best of 98)
! wall 0.133518 comb 0.140000 user 0.130000 sys 0.010000 (max of 98)
! wall 0.102381 comb 0.102449 user 0.098265 sys 0.004184 (avg of 98)
! wall 0.101891 comb 0.090000 user 0.090000 sys 0.000000 (median of 98)
Mean of the medians: 0.100587
On the present changeset:
! wall 0.091344 comb 0.090000 user 0.090000 sys 0.000000 (best of 100)
! wall 0.122728 comb 0.120000 user 0.110000 sys 0.010000 (max of 100)
! wall 0.093268 comb 0.093300 user 0.089300 sys 0.004000 (avg of 100)
! wall 0.092567 comb 0.100000 user 0.090000 sys 0.010000 (median of 100)
! wall 0.093294 comb 0.080000 user 0.080000 sys 0.000000 (best of 100)
! wall 0.144887 comb 0.150000 user 0.140000 sys 0.010000 (max of 100)
! wall 0.097708 comb 0.097700 user 0.093400 sys 0.004300 (avg of 100)
! wall 0.094980 comb 0.100000 user 0.090000 sys 0.010000 (median of 100)
! wall 0.091262 comb 0.090000 user 0.080000 sys 0.010000 (best of 100)
! wall 0.123772 comb 0.130000 user 0.120000 sys 0.010000 (max of 100)
! wall 0.093188 comb 0.093200 user 0.089300 sys 0.003900 (avg of 100)
! wall 0.092364 comb 0.100000 user 0.090000 sys 0.010000 (median of 100)
Mean of the medians is 0.0933
Differential Revision: https://phab.mercurial-scm.org/D5358
#require tla symlink
$ tla my-id "mercurial <mercurial@mercurial-scm.org>"
$ echo "[extensions]" >> $HGRCPATH
$ echo "convert=" >> $HGRCPATH
create tla archive
$ tla make-archive tla@mercurial--convert `pwd`/hg-test-convert-tla
initialize tla repo
$ mkdir tla-repo
$ cd tla-repo/
$ tla init-tree tla@mercurial--convert/tla--test--0
$ tla import
* creating version tla@mercurial--convert/tla--test--0
* imported tla@mercurial--convert/tla--test--0
create initial files
$ echo 'this is a file' > a
$ tla add a
$ mkdir src
$ tla add src
$ cd src
$ dd count=1 if=/dev/zero of=b > /dev/null 2> /dev/null
$ tla add b
$ tla commit -s "added a file, src and src/b (binary)"
A/ .arch-ids
A/ src
A/ src/.arch-ids
A .arch-ids/a.id
A a
A src/.arch-ids/=id
A src/.arch-ids/b.id
A src/b
* update pristine tree (tla@mercurial--convert/tla--test--0--base-0 => tla--test--0--patch-1)
* committed tla@mercurial--convert/tla--test--0--patch-1
create link file and modify a
$ ln -s ../a a-link
$ tla add a-link
$ echo 'this a modification to a' >> ../a
$ tla commit -s "added link to a and modify a"
A src/.arch-ids/a-link.id
A src/a-link
M a
* update pristine tree (tla@mercurial--convert/tla--test--0--patch-1 => tla--test--0--patch-2)
* committed tla@mercurial--convert/tla--test--0--patch-2
create second link and modify b
$ ln -s ../a a-link-2
$ tla add a-link-2
$ dd count=1 seek=1 if=/dev/zero of=b > /dev/null 2> /dev/null
$ tla commit -s "added second link and modify b"
A src/.arch-ids/a-link-2.id
A src/a-link-2
Mb src/b
* update pristine tree (tla@mercurial--convert/tla--test--0--patch-2 => tla--test--0--patch-3)
* committed tla@mercurial--convert/tla--test--0--patch-3
b file to link and a-link-2 to regular file
$ rm -f a-link-2
$ echo 'this is now a regular file' > a-link-2
$ ln -sf ../a b
$ tla commit -s "file to link and link to file test"
fl src/b
lf src/a-link-2
* update pristine tree (tla@mercurial--convert/tla--test--0--patch-3 => tla--test--0--patch-4)
* committed tla@mercurial--convert/tla--test--0--patch-4
move a-link-2 file and src directory
$ cd ..
$ tla mv src/a-link-2 c
$ tla mv src test
$ tla commit -s "move and rename a-link-2 file and src directory"
D/ src/.arch-ids
A/ test/.arch-ids
/> src test
=> src/.arch-ids/a-link-2.id .arch-ids/c.id
=> src/a-link-2 c
=> src/.arch-ids/=id test/.arch-ids/=id
=> src/.arch-ids/a-link.id test/.arch-ids/a-link.id
=> src/.arch-ids/b.id test/.arch-ids/b.id
* update pristine tree (tla@mercurial--convert/tla--test--0--patch-4 => tla--test--0--patch-5)
* committed tla@mercurial--convert/tla--test--0--patch-5
$ cd ..
converting tla repo to Mercurial
$ hg convert tla-repo tla-repo-hg
initializing destination tla-repo-hg repository
analyzing tree version tla@mercurial--convert/tla--test--0...
scanning source...
sorting...
converting...
5 initial import
4 added a file, src and src/b (binary)
3 added link to a and modify a
2 added second link and modify b
1 file to link and link to file test
0 move and rename a-link-2 file and src directory
$ tla register-archive -d tla@mercurial--convert
$ glog()
> {
> hg log -G --template '{rev} "{desc|firstline}" files: {files}\n' "$@"
> }
show graph log
$ glog -R tla-repo-hg
o 5 "move and rename a-link-2 file and src directory" files: c src/a-link src/a-link-2 src/b test/a-link test/b
|
o 4 "file to link and link to file test" files: src/a-link-2 src/b
|
o 3 "added second link and modify b" files: src/a-link-2 src/b
|
o 2 "added link to a and modify a" files: a src/a-link
|
o 1 "added a file, src and src/b (binary)" files: a src/b
|
o 0 "initial import" files:
$ hg up -q -R tla-repo-hg
$ hg -R tla-repo-hg manifest --debug
c4072c4b72e1cabace081888efa148ee80ca3cbb 644 a
0201ac32a3a8e86e303dff60366382a54b48a72e 644 c
c0067ba5ff0b7c9a3eb17270839d04614c435623 644 @ test/a-link
375f4263d86feacdea7e3c27100abd1560f2a973 644 @ test/b