Mail Archives: djgpp/1997/12/15/06:31:30
From: | Michael Krause <mhkrause AT umich DOT edu>
|
Newsgroups: | comp.os.msdos.djgpp
|
Subject: | Re: Slow MOV opcode
|
Date: | Sun, 14 Dec 1997 22:01:58 -0800
|
Organization: | University of Michigan
|
Lines: | 64
|
Message-ID: | <3494C7D5.9305B6CA@umich.edu>
|
References: | <01bd08e7$dfe77f00$10fbffc2 AT fsl22 DOT novo DOT dk>
|
NNTP-Posting-Host: | burlsey-217-44.reshall.umich.edu
|
Mime-Version: | 1.0
|
To: | djgpp AT delorie DOT com
|
DJ-Gateway: | from newsgroup comp.os.msdos.djgpp
|
This is a multi-part message in MIME format.
--------------9D7B7D08FBB4C182952A2B34
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Flemming Stig Larsen wrote:
<snip>
> This unuseable loop:
> __asm__ __volatile__ (
> "1:movb %%al, (%%edi)
> incl %%edi
> incl %%eax
> decl %%ecx
> jnz 1b"
> : : "ecx" (60000), "D" (video_buffer) : "ecx", "eax", "edi" );
>
> seemed to take about 19 - 20 clocks per cycle ! ouch!!
>
> while this:
> __asm__ __volatile__ (
> "1:incl %%edi
> incl %%eax
> decl %%ecx
> jnz 1b"
> : : "ecx" (60000), "D" (video_buffer) : "ecx", "eax", "edi" );
>
> only took about 2 clocks p. cycle !!!
> (must be the pairing!)
>
> **WHY** is that mov opcode so slow? can anyone explain that to me?
> **WHAT** can i do to make it faster?????
>
> Help me
>
> -Lars (reach me at: flemming DOT larsen AT private DOT dk )
You're writing to video memory. Video memory accesses can take from two
to ten times longer than regular memory accesses. Try to point edi to
something else instead, and time it.
--------------9D7B7D08FBB4C182952A2B34
Content-Type: text/x-vcard; charset=us-ascii; name="vcard.vcf"
Content-Transfer-Encoding: 7bit
Content-Description: Card for Michael Krause
Content-Disposition: attachment; filename="vcard.vcf"
begin: vcard
fn: Michael Krause
n: Krause;Michael
org: University of Michigan
adr: 6222 Douglas House Bursley Hall;;1931 Duffield St.;Ann Arbor;MI;48109;USA
email;internet: mhkrause AT umich DOT edu
title: Student
tel;home: (313)-763-2619
x-mozilla-cpt: ;0
x-mozilla-html: FALSE
version: 2.1
end: vcard
--------------9D7B7D08FBB4C182952A2B34--
- Raw text -