On Sun, Sep 05, 2021 at 04:20:02PM +0800, ZheNing Hu wrote:
> > + if (ref_cbdata->filter->streaming_format) {
> > + pretty_print_ref(refname, oid, ref_cbdata->filter->streaming_format);
>
> So we directly use pretty_print_ref() in streaming mode, OK.
>
> > + } else {
> > + /*
> > + * We do not open the object yet; sort may only need refname
> > + * to do its job and the resulting list may yet to be pruned
> > + * by maxcount logic.
> > + */
> > + ref = ref_array_push(ref_cbdata->array, refname, oid);
> > + ref->commit = commit;
> > + ref->flag = flag;
> > + ref->kind = kind;
> > + }
> >
> > return 0;
> > }
>
> Therefore, in streaming mode, there is no need to push ref to
> ref_array, which can
> reduce the overhead of malloc(), free(), which makes sense.
By the way, one thing I wondered here: how much of the benefit is from
avoiding the ref_array, and how much is from skipping the sort entirely.
It turns out that most of it is from the latter. If I do this:
diff --git a/builtin/for-each-ref.c b/builtin/for-each-ref.c
index 89cb6307d4..037d5db814 100644
--- a/builtin/for-each-ref.c
+++ b/builtin/for-each-ref.c
@@ -78,7 +78,11 @@ int cmd_for_each_ref(int argc, const char **argv, const char *prefix)
filter.name_patterns = argv;
filter.match_as_path = 1;
filter_refs(&array, &filter, FILTER_REFS_ALL | FILTER_REFS_INCLUDE_BROKEN);
- ref_array_sort(sorting, &array);
+ /*
+ * we should skip this only when we are using the default refname
+ * sorting, but as an experimental hack, we'll just comment it out.
+ */
+ // ref_array_sort(sorting, &array);
if (!maxcount || array.nr < maxcount)
maxcount = array.nr;
then the timings I get are:
Benchmark #1: ./git.old for-each-ref --format='%(objectname) %(refname)'
Time (mean ± σ): 341.4 ms ± 7.4 ms [User: 299.8 ms, System: 41.6 ms]
Range (min … max): 333.5 ms … 355.1 ms 10 runs
Benchmark #2: ./git.new for-each-ref --format='%(objectname) %(refname)'
Time (mean ± σ): 249.1 ms ± 5.7 ms [User: 211.8 ms, System: 37.2 ms]
Range (min … max): 245.9 ms … 267.0 ms 12 runs
Summary
'./git.new for-each-ref --format='%(objectname) %(refname)'' ran
1.37 ± 0.04 times faster than './git.old for-each-ref --format='%(objectname) %(refname)''
So of the 1.5x improvement that the original patch showed, 1.37x is from
skipping the sort of the already-sorted data. I suspect that has less to
do with sorting at all, and more to do with the fact that even just
formatting "%(refname)" for each entry takes a non-trivial amount of
time.
-Peff
