Date: Thu, 3 Nov 1994 10:15:10 -0500 (EST)
From: Ed Phillips <flaregun AT udel DOT edu>
To: Charles Sandmann <sandmann AT new-orleans DOT NeoSoft DOT com>
Cc: Sean Smith <S DOT D DOT Smith AT ecs DOT soton DOT ac DOT uk>, djgpp AT sun DOT soe DOT clarkson DOT edu,
        jnc AT ecs DOT soton DOT ac DOT uk
Subject: Re: Disk I/O rates with DJGPP

On Wed, 2 Nov 1994, Charles Sandmann wrote:

> > A colleague of mine who is also using DJGPP has commented that the disk I/O
> > (low level) for DJGPP objects is substantially slower than native 
> > Windows or DOS I/O. The comment is that e.g. Zortech C/C++ can produce
> > binaries that give block reads and writes of large blocks at up to
> > 400kbs-1 while despite the chosen blocksize DJGPP low level reads and
> > writes reach a ceiling at around 30kbs-1. Obviously there is some
> > h/w dependency here, but I guess the ratios are comparable whatever the
> > hardware.
> > 
> > I'm just off to look at the sources for read/write now, but does anyone
> > have any comments on this?
> 
> I did some rather extensive benchmark testing in V2.x development on this
> subject (both with and without disk caches).  I compared TCC, low-level
> DOS, and DJGPP V1.x and V2.x.  A bug fix which improved V1.11 throughput
> was implemented in one of the V1.11maint releases.
> 
> The short answer is our transfer buffer is too small.  This is not
> changeable in V1.x but can be stubedited in V2.x.  I was able to read 
> over 1Mb/sec into DJGPP with V2.0 code on large contig files on a 32Kb
> transfer buffer (on a real disk, faster on RAM disk).  This was actually
> about the same speed as the TCC or low level dos at that point.
> 
> If you really want speed, you can use the _go32_dpmi calls to allocate
> your own 32Kb real buffer and do the reads manually.
> 

	Could you post some example code showing how to do this?  That 
may be enough for people to be content until version 2.0 is ready. :-)
Something like this would be nice:

int fastread(int fd, void *buf, int buflen)
{
	...
}

	Thanks,
	Ed

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/* Ed Phillips  flaregun AT udel DOT edu              University of Delaware       */
/* Jr Systems Programmer  (302) 831-6082    IT/Network and Systems Services */
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