Date: Tue, 31 Aug 1999 12:17:31 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: Kevin Street <street@iname.com> Cc: Soren Schmidt <sos@freebsd.dk>, current@FreeBSD.ORG Subject: Re: HEADS UP! ATA driver (atapi DMA).. Message-ID: <199908311917.MAA26255@apollo.backplane.com> References: <199908311213.OAA80049@freebsd.dk> <87btbnetgc.fsf@mired.eh.local> <199908311759.KAA25628@apollo.backplane.com> <87906repae.fsf@mired.eh.local>
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:Matthew Dillon <dillon@apollo.backplane.com> writes:
:
:> :Two things I've noticed:
:> :1) my cdrom delivers about 2M/s which is the same as before DMA. Is
:> :the improvement only in cpu usage or should I be seeing a speed
:> :improvement too?
:> :
:> :speed tested with:
:> :dd if=/dev/racd0c of=/dev/null bs=64k count=320
:> :(I get it to spin up with another dd before this test)
:>
:> Well 2MB/sec == 14x CDRom drive. Is it a 14x CDRom drive? CDRom
:> drives are typically limited to how quickly they can get data off
:> the platter. A faster bus transfer will not improve that.
:
:I should have mentioned that ... it's a 32x cdrom. dmesg says it
:claims to be able to do 5515 KB/sec.
:
:I've played around with using dd ... skip=n to reposition which part
:of the cd I'm reading and I've seen some much better speeds on the
:outer tracks (I think I now recall that cd's start numbering from the
:inside tracks, don't they?). So you're probably right that it's just
:the rotational speed that I was seeing.
:
:--
:Kevin Street
:street@iname.com
Dunno re: starting track.
All modern CDRom units have vibration sensors (actually I think they
just use the error rate from the head) and will adjust the rotational
speed based on that as well as on the rate the data is being requested
at. So it will depend on the physical CD as well as other matters.
-Matt
Matthew Dillon
<dillon@backplane.com>
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