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References: <39EE49FE-23A5-43DE-8998-51526287D182@larrygritz.com>
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From: Craig Bruce <csbruce@cubewerx.com>
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Date: Mon, 15 Jan 2018 21:09:52 -0400
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Subject: Re: [Tiff] Strategies for multi-core speedups
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    <div class="moz-cite-prefix">On 01/15/2018 08:15 PM, Bob Friesenhahn
      wrote:<br>
    </div>
    <blockquote type="cite"
      cite="mid:alpine.GSO.2.20.1801151728170.18206@scrappy.simplesystems.org">
      <pre wrap="">On Mon, 15 Jan 2018, Mike Stanton wrote:
</pre>
      <blockquote type="cite">
        <pre wrap="">To begin with I am an Operating Systems guy.  When you are looking 
at going to multi-threading, what have you determined as your 
setup/teardown cost for the individual threads? How large a chunk 
will each thread be processing?  Will the individual Scan-lines 
and/or Tiles be sufficiently large to absorb the cost of that setup 
and teardown by the inherent performance you are projecting?
</pre>
      </blockquote>
      <pre wrap="">It is normal to use a pool of threads where threads are created in 
advance (or added to the pool on demand) and obtained from, and 
returned to, the pool.  This significantly reduces overheads caused by 
starting/stopping threads.</pre>
    </blockquote>
    Creating and destroying threads ought to take on the scale of a few
    microseconds (on Linux anyway).  Larry Gritz was saying it takes
    16.2 seconds to read what could be 1024 tiles of size 256×256, which
    is 15.8 ms per tile, which is nearly four orders of magnitude longer
    than thread creation for reading.  Writing with Deflate compression
    is about an order of magnitude slower than reading.<br>
    <br>
    However, you don't need to launch a new thread for every tile if you
    just break up the job into N=number_of_cpus pieces and launch N
    threads where each is pre-assigned to read or write a particular
    group of tiles of the overall image.  The thread-creation overhead
    would be around six or seven orders of magnitude smaller than the
    reading or writing.<br>
    <br>
    <div class="moz-signature">-- <br>
      Dr. Craig S. Bruce
      <br>
      Senior Software Developer
      <br>
      CubeWerx<i> </i>Inc.
      <br>
      <a href="http://www.cubewerx.com/">http://www.cubewerx.com</a></div>
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