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Apple OSes and IDE DMA Support?
KFox wishes to get to the core of this particular issue: "I just recently purchased an iBook and I have noticed that even in Jaguar, the system gets choppy from disk I/O. It appears that Mac OS 9 and Mac OS X don't support DMA access for hard drives, even if the drives are initialized in a UDMA mode. Wintel has had support in this area for a long time (since Win95b). Has anyone in the Mac world had any experience with DMA support on hard drives? Is it supported on iBooks? If so, which models?"
The ChangeLog seems to have added UDMA in version 1.1 and later updated in 1.7 .
Try searching for UDMA Ultra-ATA ATA33/66/100 because DMA doesnt allways show up.
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Daemon News has a little section on the iBook and DMA. You can see the Darwin boot sequence by holding down the "v" key at startup. Find the section titled "Further Exploration: Das Boot" in the article above and it will tell you how to view the boot messages and other useful tidbits.
It appears that this revision-A iBook does indeed have DMA enabled for both the hard drive and the CD-ROM drive.
This does not help you enable your own DMA, but do a search on Google for enabling DMA on FreeBSD style systems. You might find something useful.
Are you sure it's the disk causing the problem vs delays due to VM switching in and out. There's a memory utility (can't remember name, Memory Tracker or Memory Monitor?) that will beep each time memory is paged in or out (or you could use top if you can interpret the numbers).
I've found it can be pretty easy to use up all free RAM if you have a number of programs open or they leak memory. I've found at times I've had over 2GB of switch files.
This is with 896 MB of RAM, iBooks can be under spec'd in that department.
# sysctl -a | grep dma
/etc/sysctl.conf to make it enable it on every boot also.
Look for a setting that's related to DMA and set it from 0 to 1 with "sysctl -w". You should be able to place the setting in
Unfortunately, I don't have an OSX box to test it on right now, so I can't give you the exact settings. OSX is based on FreeBSD, and FreeBSD enables DMA by default, however, it's possible that apple found a need to disable it by default. Some drive/chipset combos have problems with DMA, and if they were unsure of which brands of drives or chipsets they would be using, disabling it by default would be the safe way to go.
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Will someone please mod up comment #4222630??? The most likely answer is KFox hasn't bought enough RAM.
Run this command from the Mac OS X shell:
dd if=/dev/zero of=testfile bs=1024 count=102400
This should make you a 100 MB file. dd on some systems will give you how long it took to write out the file in seconds (I don't have access to a Mac OS X box, just a FreeBSD box right now). If it doesn't, just put the time command in front of it:
time dd if=/dev/zero of=testfile bs=1024 count=102400
Devide the number of seconds it took to write the file out by 100, and you'll have a rough estimate of how many megabytes per second it wrote to disk.
Again, not the most comprehensive metric of course, but it gives you a rough idea. For an ATA system, it should probably do between 15 and 25 MB/s without too much trouble for a fast drive. The interface can be much faster (ATA/33, ATA/66, ATA/100), but the UFS and HFS+ file systems aren't optimized for sequntial writing, and/or there are other factors involved, so about 20 MB/s is a good mark I think.
My iMac certainly feels slow, but I don't think it's disk DMA. "dd bs=8k count=100000 >ttt /dev/zero" gives a speed of 30MB/s which would be impossible without DMA.
Anyone know a way to check whether ATA write caching is enabled? The FreeBSD ATA sysctls don't work, presumably it's not using the FreeBSD ATA drivers.
Mac's have had DMA support for a long time in both hardware and software, see this technote and the Developer Notes on hardware here for details. This includes the original clamshell iBooks. The iBooks may not have the fastest drives or interfaces but I don't think this is the problem. It's much more likely a Virtual Memory issue with lots of caching going on. check the contents of /private/var/vm/ for the number of 80Mb swapfiles you have, also try issuing vm_stat from the CLI to see whats going on. Two suggestions, either get more RAM or setup a 'clean' swap-drive partition.
The linux IDE driver has an option which controls whether it masks or unmasks non-ide interrupts during disk transfers...this option makes a huge difference in the amount of cpu time disk access consumes.
Does OS X have something similar?
But, as someone else pointed out. Linux, and X still seems to run faster, which is pretty ridiculous, considering that X is running through a socket, and is naturally indirect. *sigh*
I'm not sure of the technical details, but my understanding is that Quartz works very much the same way - although Apple doesn't seem to provide a way to do it, it should be possible to run applications remotely, just like you can with X.
$x='S24;r)>63/* h@<5+oZ)32"5cz';$me='phroggy'x$];
$x=~y+ -xz+\0-Tx+;print$_^chop$me for split'',$x;
The year is 2002. I simply will not "wait" for my computer. The computer is supposed to wait for me, yet I find myself waiting on OS X, especially when running web browsers.