C/UNIX low level I/O

[Gordon Cross]

In article <6695 at pyr.gatech.EDU>, david at pyr.gatech.EDU (David Brown) writes:
> 
>  Hi, NetLanders.  I've a small C/UNIX problem.  I need to do a bunch of
>  small write's to a file.  I need to know the quickest way to do it.
>  I've got a linked list of 'words' that I need written to a file in a 
>  humanly readable and understandable fashion.  But it needs to take as
>  little time as possible.  For instance, the way I have it now, I use
>  write(2).  But this ay, I do a separate 'write' for every word in the
>  list, and a 'write' for the spaces between and the newlines.

I've had some experience doing a similiar thing myself.  I acheived a
significant increase in throughput by filling a memory buffer with the image
of the data I wished to write out and then doing a single write(2) for the
whole buffer.  The reason this is faster is that each call to write(2) requires
a process context switch to the kernal to service the request.  The disk
controller itself can slow you down if it is called on repeatedly to do small
operations.  I could rant on and on about why this is the case but you should
have the general idea.  Also your buffer should be at least the size of a 
disk block or multiple thereof.  Good luck!


Gordon Cross
Intergraph Corp.  Huntsville, AL