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Subject:	Re: xz-5.2.2: No threaded compression
To:	cygwin AT cygwin DOT com
References:	<550c836a-b321-b8e4-6fb6-b2e3751f6da1 AT tiscali DOT co DOT uk> <dba125cf-9664-19bc-083f-e3d13560e569 AT cygwin DOT com>
From:	David Stacey <drstacey AT tiscali DOT co DOT uk>
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Date:	Wed, 10 May 2017 06:33:23 +0100
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On 10/05/17 01:15, Yaakov Selkowitz wrote:
> On 2017-05-09 18:02, David Stacey wrote:
>> The man page for xz suggests that threaded compression ought to be
>> available. However, when I run 'xz --threads=0 <file>' only one CPU core
>> is used. Is there a way that I can run parallel xz compression in 
>> Cygwin?
>
> WFM.  Note from the manpage:
>
>    -T threads, --threads=threads
>        Specify the number of worker threads to use.  Setting threads to
>        a  special value 0 makes xz use as many threads as there are CPU
>        cores on the system.  The actual number of threads can  be less
>        than  threads  if the input file is not big enough for threading
>        with the given settings or if using more  threads  would exceed
>        the memory usage limit.

That's helpful, thank you. The files I'm trying to compress are several 
GB, so I suppose I must be hitting the memory limit - which is 
surprising, given that I'm on a 64-bit system with a fair amount of RAM. 
I'll take a look at the source code and see if I can figure out what 
criteria it uses to enable or disable threaded compression.

Thanks again,

Dave.


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