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Date:      Tue, 30 May 2017 06:55:02 -0400
From:      "Chad J. Milios" <milios@ccsys.com>
To:        Koichiro IWAO <meta@vmeta.jp>, freebsd-questions <freebsd-questions@freebsd.org>
Subject:   Re: Is it possible to use more than 1 CPUs during pkg create?
Message-ID:  <D75F743F-D5F9-42EB-BE24-7A7A3C14B96E@ccsys.com>
In-Reply-To: <0101015c58b3dc58-1b936a1a-8412-472b-a257-c436a40e89f2-000000@us-west-2.amazonses.com>
References:  <0101015c58b3dc58-1b936a1a-8412-472b-a257-c436a40e89f2-000000@us-west-2.amazonses.com>

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> On May 30, 2017, at 5:33 AM, Koichiro IWAO <meta@vmeta.jp> wrote:
>=20
> Hi,
>=20
> is it possible to use more than 1 CPU cores during xz compression
> done in pkg create? I know XZ Utils in base system can use more
> than 1 CPUs if -T option given. I guess pkg internally calls APIs
> of XZ Utils. I think it is potentially possible.
>=20
> Or is it restricted to use only 1 CPU core for some reasons?
>=20
>=20
> --=20
> `whois vmeta.jp | nkf -w`
> meta <meta@vmeta.jp>

Threading forfeits a bit of xz=E2=80=99s great compression ratio. An xz =
file created with -T greater than 1 will necessarily be some amount =
larger. Operating with just one thread achieves the maximal compression =
ratio. (The multiple compression threads fail to share the dictionaries =
they are currently building.)

When you are transferring GBytes to yourself once, use -T0. When you are =
compressing something one time that hundreds or thousands of people will =
potentially download and/or store, use -T1 (the default).=



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