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From: Jeff King <peff@peff.net>
To: "brian m. carlson" <sandals@crustytoothpaste.net>,
	git@vger.kernel.org, Martin Ågren <martin.agren@gmail.com>,
	Junio C Hamano <gitster@pobox.com>
Subject: Re: [PATCH 0/5] tree-walk object_id refactor
Date: Fri, 11 Jan 2019 09:17:53 -0500
Message-ID: <20190111141753.GA16754@sigill.intra.peff.net> (raw)
In-Reply-To: <20190111001750.GO423984@genre.crustytoothpaste.net>

On Fri, Jan 11, 2019 at 12:17:50AM +0000, brian m. carlson wrote:

> > I think this is really the only safe and sane solution. We resisted it
> > because of the cost of the extra copies (especially the
> > update_tree_entry() one). But I don't know that anybody actually
> > measured it. Do you have any performance numbers before/after this
> > series?
> 
> Unfortunately, I don't. I'm not really sure in what situations we hit
> this code path a lot, so I'm not sure what exactly we should performance
> test. If you have suggestions, I can set up some perf tests.

I think the interesting one here is the copy in update_tree_entry(),
which is called for every entry of every tree we parse for a diff. So
the command with the most noticeable impact, I think, would be something
like:

  git log -- pathspec

I couldn't demonstrate any measurable slowdown (I didn't compute the
mean to see if it gets worse, but certainly any change is within the
run-to-run noise).

I guess that is competing with the cost to access the commit objects.
Perhaps a pure tree diff would be a more precise test. Here's the most
pathological case I could come up with:

  git init
  for i in $(seq 10000); do echo $i >$i; done
  git add .
  git commit -m base
  echo change >9999
  git commit -am change
  time git diff-tree HEAD^ HEAD

which should really be spending 99% of its time inflating and walking
through the trees. And even there I couldn't measure anything.

So I'd say it's probably fine.

-Peff

  reply index

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-07 23:34 What's cooking in git.git (Jan 2019, #01; Mon, 7) Junio C Hamano
2019-01-08  9:50 ` tg/checkout-no-overlay, was " Thomas Gummerer
2019-01-08 17:51   ` Junio C Hamano
2019-01-08 17:30 ` ag/sequencer-reduce-rewriting-todo " Alban Gruin
2019-01-08 21:20 ` sb/more-repo-in-api, was " Jonathan Tan
2019-01-08 21:35   ` Junio C Hamano
2019-01-09 21:28     ` Stefan Beller
2019-01-09  7:37 ` Martin Ågren
2019-01-09 21:06   ` Martin Ågren
2019-01-10  1:02     ` brian m. carlson
2019-01-10 18:55       ` Junio C Hamano
2019-01-10 19:03       ` Martin Ågren
2019-01-10  4:25     ` [PATCH 0/5] tree-walk object_id refactor brian m. carlson
2019-01-10  4:25       ` [PATCH 1/5] tree-walk: copy object ID before use brian m. carlson
2019-01-10  4:25       ` [PATCH 2/5] match-trees: compute buffer offset correctly when splicing brian m. carlson
2019-01-10  4:25       ` [PATCH 3/5] match-trees: use hashcpy to splice trees brian m. carlson
2019-01-10  6:45         ` Jeff King
2019-01-10 23:55           ` brian m. carlson
2019-01-11 14:51             ` Jeff King
2019-01-11 14:54               ` Jeff King
2019-01-14  1:30                 ` brian m. carlson
2019-01-14 15:40                   ` Jeff King
2019-01-10  4:25       ` [PATCH 4/5] tree-walk: store object_id in a separate member brian m. carlson
2019-01-10  6:49         ` Jeff King
2019-01-10 23:57           ` brian m. carlson
2019-01-10  4:25       ` [PATCH 5/5] cache: make oidcpy always copy GIT_MAX_RAWSZ bytes brian m. carlson
2019-01-10  6:50         ` Jeff King
2019-01-10  6:40       ` [PATCH 0/5] tree-walk object_id refactor Jeff King
2019-01-11  0:17         ` brian m. carlson
2019-01-11 14:17           ` Jeff King [this message]
2019-01-15  0:39     ` [PATCH v2 " brian m. carlson
2019-01-15  0:39       ` [PATCH v2 1/5] tree-walk: copy object ID before use brian m. carlson
2019-01-15  0:39       ` [PATCH v2 2/5] match-trees: compute buffer offset correctly when splicing brian m. carlson
2019-01-15  0:39       ` [PATCH v2 3/5] match-trees: use hashcpy to splice trees brian m. carlson
2019-01-15  0:39       ` [PATCH v2 4/5] tree-walk: store object_id in a separate member brian m. carlson
2019-01-15  0:39       ` [PATCH v2 5/5] cache: make oidcpy always copy GIT_MAX_RAWSZ bytes brian m. carlson
2019-01-15 17:51       ` [PATCH v2 0/5] tree-walk object_id refactor Junio C Hamano
2019-01-09 10:28 ` What's cooking in git.git (Jan 2019, #01; Mon, 7) Jeff King
2019-01-10 19:05   ` Junio C Hamano
2019-01-10 19:46   ` Junio C Hamano
2019-01-10 18:02 ` Stefan Beller

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