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From: Jeff King <peff@peff.net>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Junio C Hamano <gitster@pobox.com>,
	Marc Stevens <marc.stevens@cwi.nl>,
	Dan Shumow <danshu@microsoft.com>,
	Git Mailing List <git@vger.kernel.org>
Subject: Re: [PATCH] Put sha1dc on a diet
Date: Wed, 1 Mar 2017 14:53:02 -0500	[thread overview]
Message-ID: <20170301195302.3pybakmjqztosohj@sigill.intra.peff.net> (raw)
In-Reply-To: <CA+55aFx1wAS-nHS2awuW2waX=cvig4UoZqmN5H3v93yDE7ukyQ@mail.gmail.com>

On Wed, Mar 01, 2017 at 10:49:55AM -0800, Linus Torvalds wrote:

> That said, I think that it would be lovely to just default to
> USE_SHA1DC and just put the whole attack behind us. Yes, it's slower.
> No, it doesn't really seem to matter that much in practice.

My biggest concern is the index-pack operation. Try this:

  time git clone --no-local --bare linux tmp.git

with and without USE_SHA1DC. I get:

  [w/ openssl]
  real	1m52.307s
  user	2m47.928s
  sys	0m14.992s

  [w/ sha1dc]
  real	3m4.043s
  user	6m16.412s
  sys	0m13.772s

That's real latency the user will see. It's hard to break it down,
though. The actual "receiving" phase is generally going to be network
bound. The delta-resolution that happens afterwards is totally local and
CPU-bound (but does run in parallel).

And of course this repository tends to the larger side (though certainly
there are bigger ones), and you only feel the pain on clone or when
doing an initial push, not day-to-day.

So maybe we just suck it up and accept that it's a bit slower.

-Peff

  parent reply	other threads:[~2017-03-01 20:02 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-03-01  0:30 [PATCH] Put sha1dc on a diet Linus Torvalds
2017-03-01 18:42 ` Junio C Hamano
2017-03-01 18:49   ` Linus Torvalds
2017-03-01 19:41     ` Junio C Hamano
2017-03-01 21:56       ` Johannes Schindelin
2017-03-01 22:05         ` Junio C Hamano
2017-03-01 22:16         ` Linus Torvalds
2017-03-01 22:51           ` Johannes Schindelin
2017-03-01 23:05             ` Linus Torvalds
2017-03-01 23:19               ` Jeff King
2017-03-02  6:10                 ` Duy Nguyen
2017-03-02 14:45                   ` Johannes Schindelin
2017-03-02 16:35                     ` Linus Torvalds
2017-03-02 18:37                       ` Jeff Hostetler
2017-03-02 19:04                         ` Linus Torvalds
2017-03-02 14:39                 ` Johannes Schindelin
2017-03-02 14:37               ` Johannes Schindelin
2017-03-01 19:53     ` Jeff King [this message]
     [not found]       ` <CA+55aFwf3sxKW+dGTMjNAeHMOf=rvctEQohm+rbhEb=e3KLpHw@mail.gmail.com>
2017-03-01 20:34         ` Jeff King
     [not found]           ` <CA+55aFwr1jncrk-cekn0Y8rs_S+zs7RrgQ-Jb-ZbgCvmVrHT_A@mail.gmail.com>
2017-03-01 23:13             ` Jeff King
2017-03-01 23:38           ` Linus Torvalds
2017-03-02  1:31             ` Dan Shumow
2017-03-02  4:38               ` Junio C Hamano
2017-03-04  1:07                 ` Dan Shumow
2017-03-13 15:13                   ` Jeff King
     [not found]                     ` <CY1PR0301MB2107B3C5131D5DC7F91A0147C4250@CY1PR0301MB2107.namprd03.prod.outlook.com>
     [not found]                       ` <CY1PR0301MB2107876B6E47FBCF03AB1EA1C4250@CY1PR0301MB2107.namprd03.prod.outlook.com>
2017-03-13 19:48                         ` Jeff King
2017-03-13 20:12                           ` Marc Stevens
2017-03-13 20:20                             ` Linus Torvalds
2017-03-13 20:47                               ` Marc Stevens
2017-03-13 21:00                                 ` Jeff King
2017-03-13 21:15                                   ` Marc Stevens
2017-03-16 18:22                                     ` Marc Stevens
2017-03-16 22:06                                       ` Jeff King
2017-03-16 22:07                                         ` Dan Shumow
2017-03-01 19:07 ` Jeff King
2017-03-01 19:10   ` Linus Torvalds

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