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what is the purpose of -Dxt3 in the makefile? [SOLVED]
Date: 2017/06/01 19:46
Name: Chris Latham

Greetings,

Some of the examples in the makefile for OpenMX 3.8.3 pass the flag -Dxt3 to the compiler, which causes a single line of code "setvbuf(fp_VC,buf,_IOFBF,fp_bsize); /* setvbuf */" to be included when it is raised. What is the purpose of this? When should it be used?

Many thanks,

Christopher.
orcid.org/0000-0003-0509-925X
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Re: what is the purpose of -Dxt3 in the makefile? ( No.1 )
Date: 2017/06/01 11:17
Name: T. Ozaki

Hi,

It was found in some IO systems that saving small amount of data frequently degrades
the performance (i.e., IO speed) significantly. To reduce the frequency of IO access,
setvbuf can be utilized very effectively. Please take a look at
https://en.wikibooks.org/wiki/C_Programming/stdio.h/setvbuf

In fact, we found that the performance can be improved in such systems.

Regards,

TO
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Re: what is the purpose of -Dxt3 in the makefile? [SOLVED] ( No.2 )
Date: 2017/06/01 19:44
Name: Chris Latham

Hello,

That's very helpful, thanks. I understand now.

It would probably be worth including a few words about this in the official installation instructions (I cannot find anything but may have missed it).

On systems with Linux kernel from 2.6.13 (or 2.6.26 for finer control) it is also possible to set, modify, and examine I/O scheduling with the ionice command (e.g. for low priority use "ionice -c 3 _command_"). See "man ionice" for details.

Many thanks again,

Christopher.
orcid.org/0000-0003-0509-925X
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