Welcome to the most active Linux Forum on the web.
Go Back > Forums > Non-*NIX Forums > Programming
User Name
Programming This forum is for all programming questions.
The question does not have to be directly related to Linux and any language is fair game.


  Search this Thread
Old 08-01-2003, 01:52 PM   #1
LQ Newbie
Registered: Aug 2003
Location: Hunstville, AL
Distribution: RedHat and custom
Posts: 2

Rep: Reputation: 0
Memory Mapped file IO problems

I've been working with a parallel IO board that sets up its own memory mapped region. I have no trouble reading and processing the data from this buffer. I'm trying to copy this data to the hard drive (large file accesses) and the process is EXTREMELY speed critical. I'm using a UDMA hard drive and the data transfers from the IO card to its memory mapped region use Demand Mode DMA accesses.

Does anyone have any suggestions on what the fastest way to copy these chunks of data is? I've tried memory mapping the file to kernel memory, but it seems like it takes longer on account of remapping the file for every subsequent chunk. (I can only get it to work if it's copied to an intermediate buffer) Here's what seems to work the best so far. It seems too simple, but isn't fast enough. Any suggestions?

/* Telling the parallel IO card (_fd) to copy the data from its buffers to a memory mapped read transfer buffer */
read(_fd, NULL, transferSize);
*** Then... ***
/* Writing the data to disk (fp) from the read transfer buffer (mmRead) */
write(fp, mmRead, transferSize);

I thought about possibly seeing if the IO card would copy directly to a memory mapped file, but I get lock ups and segmentation faults:

read(_fd, mmRead, transferSize);
*** OR ***
memcpy(mmFile, mmRead, transferSize);

Any help is GREATLY appreciated. Thanks.

Last edited by legogt; 08-01-2003 at 02:03 PM.


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Out Of Memory problems. My server is down. Memory logs attached. guarriman Linux - General 7 06-10-2008 07:46 AM
Mapped Drive Timeout KrGAce Linux - Newbie 4 01-08-2005 07:43 PM
Keyboard keys not mapped. Clumsy Slackware 1 12-15-2004 10:13 PM
Mapped Drive Time out KrGAce Linux - Enterprise 0 12-06-2004 07:17 AM
My own mapped keyb (?) erickFis Slackware 4 02-19-2004 10:53 AM > Forums > Non-*NIX Forums > Programming

All times are GMT -5. The time now is 12:08 AM.

Main Menu
Write for LQ is looking for people interested in writing Editorials, Articles, Reviews, and more. If you'd like to contribute content, let us know.
Main Menu
RSS1  Latest Threads
RSS1  LQ News
Twitter: @linuxquestions
Facebook: linuxquestions Google+: linuxquestions
Open Source Consulting | Domain Registration