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January 2016

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2016.01.25 18:25 "OpenMP enabled libtiff", by Aaron Boxer
2016.01.25 19:05 "Re: OpenMP enabled libtiff", by Aaron Boxer
2016.01.25 19:17 "Re: OpenMP enabled libtiff", by <kandel3@illinois.edu>
2016.01.25 19:18 "Re: OpenMP enabled libtiff", by Bob Friesenhahn
2016.01.25 20:21 "Re: OpenMP enabled libtiff", by Aaron Boxer
2016.01.25 20:45 "Re: OpenMP enabled libtiff", by Bob Friesenhahn
2016.01.25 23:27 "Re: OpenMP enabled libtiff", by <kandel3@illinois.edu>
2016.01.26 09:12 "Re: OpenMP enabled libtiff", by <jcupitt@gmail.com>
2016.01.26 13:45 "Re: OpenMP enabled libtiff", by Aaron Boxer
2016.01.26 14:46 "Re: OpenMP enabled libtiff", by Olivier Paquet
2016.01.26 16:01 "Re: OpenMP enabled libtiff", by Aaron Boxer
2016.01.26 17:10 "Re: OpenMP enabled libtiff", by Bob Friesenhahn
2016.01.26 19:32 "Re: OpenMP enabled libtiff", by Aaron Boxer
2016.01.26 19:29 "Re: OpenMP enabled libtiff", by Aaron Boxer
2016.01.26 20:36 "Re: OpenMP enabled libtiff", by Bob Friesenhahn
2016.01.27 18:32 "Re: OpenMP enabled libtiff", by Aaron Boxer
2016.01.27 19:55 "Re: OpenMP enabled libtiff", by Bob Friesenhahn
2016.01.29 13:28 "Re: OpenMP enabled libtiff", by Aaron Boxer
2016.01.29 14:46 "Re: OpenMP enabled libtiff", by Bob Friesenhahn
2016.01.29 15:48 "Re: OpenMP enabled libtiff", by Aaron Boxer
2016.01.29 15:49 "Re: OpenMP enabled libtiff", by Aaron Boxer
2016.01.29 18:12 "Re: OpenMP enabled libtiff", by Bob Friesenhahn
2016.01.26 09:36 "Re: OpenMP enabled libtiff", by Mat Maher
2016.01.26 09:52 "Re: OpenMP enabled libtiff", by Even Rouault
2016.01.26 14:22 "Re: OpenMP enabled libtiff", by Fred Rothganger
2016.01.27 18:51 "Re: OpenMP enabled libtiff", by Larry Gritz

2016.01.27 18:32 "Re: OpenMP enabled libtiff", by Aaron Boxer

On Tue, Jan 26, 2016 at 3:36 PM, Bob Friesenhahn <
bfriesen@simple.dallas.tx.us> wrote:

> On Tue, 26 Jan 2016, Aaron Boxer wrote:
>
>>
>> By the way, since libtiff uses memory mapped files as default,
>> using multiple handles isn't that bad, because the handles will all
>> access the same memory mapping, at least on unices.
>>
>
> Memory mapping is great if you plan to read the file more than once but if
> you plan to read the file just once, then it may impose a significant
> penalty.  This is particularly true of the file is accessed over a network
> file system.
>
> Often, there is no need to read the data more than once so using memory
> mapping wastes memory and may break the operating system's sequential
> access / read-ahead detection.  It is likely that the (smart) operating
> system knows about file handles and tries to deduce the current behavior
> (e.g. sequential vs random access) of each file handle so as to know if or
> how much read-ahead should be done.  TIFF is a strange format since it
> requires both sequential and random access behavior, unless one uses
> multiple file descriptors and the data is nicely ordered.  Using multiple
> file descriptors (one to access IFDs and the other to read strip/tile data)
> may offer significant performance benefits.



Thanks, Bob. So, are you saying that as TIFF is currently designed, memory
mapping is beneficial  ? Because of the random access ?
This was my experience on windows : turning off memory mapping when using
libtiff degraded performance.

My other question is : why is unix and windows treated differently in
tifflib?  mmap call allows sharing of mapping between different file
handles, while on windows this is turned off. I think it would be nice to
have on windows.

Cheers,
Aaron




>
>
> Bob
> --
> Bob Friesenhahn
> bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
> GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/
>