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From: Jeff King <peff@peff.net>
To: ZheNing Hu <adlternative@gmail.com>
Cc: Git List <git@vger.kernel.org>
Subject: Re: [PATCH 1/2] ref-filter: hacky "streaming" mode
Date: Sun, 5 Sep 2021 09:15:04 -0400	[thread overview]
Message-ID: <YTTC2IUO1ZmTOEoR@coredump.intra.peff.net> (raw)
In-Reply-To: <CAOLTT8Tka0nxHb3G9yb-fs8ue7RaPCUVSKi5PM+GY+rMjFRnog@mail.gmail.com>

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

  parent reply	other threads:[~2021-09-05 13:15 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-04 12:40 [hacky PATCH 0/2] speeding up trivial for-each-ref invocations Jeff King
2021-09-04 12:41 ` [PATCH 1/2] ref-filter: hacky "streaming" mode Jeff King
2021-09-05  8:20   ` ZheNing Hu
2021-09-05 13:04     ` Jeff King
2021-09-07  5:28       ` ZheNing Hu
2021-09-07 18:01         ` Jeff King
2021-09-09 14:45           ` ZheNing Hu
2021-09-10 14:26             ` Jeff King
2021-09-15 12:27               ` ZheNing Hu
2021-09-15 14:23                 ` ZheNing Hu
2021-09-16 21:45                   ` Jeff King
2021-09-20  7:42                     ` ZheNing Hu
2021-09-16 21:31                 ` Jeff King
2021-09-05 13:15     ` Jeff King [this message]
2021-09-07  5:42       ` ZheNing Hu
2021-09-04 12:42 ` [PATCH 2/2] ref-filter: implement "quick" formats Jeff King
2021-09-05  8:20   ` ZheNing Hu
2021-09-05 13:07     ` Jeff King
2021-09-06 13:34       ` ZheNing Hu
2021-09-07 20:06       ` Junio C Hamano
2021-09-05  8:19 ` [hacky PATCH 0/2] speeding up trivial for-each-ref invocations ZheNing Hu
2021-09-05 12:49   ` Jeff King
2021-09-06 13:30     ` ZheNing Hu
2021-09-07 17:28       ` Jeff King
2021-09-09 13:20         ` ZheNing Hu
2021-09-06  6:54 ` Patrick Steinhardt

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