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SubjectRe: PROMBLEM: CD burning at 16x uses excessive CPU, although DMA is enabled
On Tue, 9 Apr 2002, Roger Larsson wrote:

> On tisdagen den 9 april 2002 12.01, Anssi Saari wrote:
> > On Mon, Apr 08, 2002 at 06:02:55PM -0400, Mark Hahn wrote:
> > > I think someone else already pointed out that doing
> > > a kernel profile would be good. strace would also
> > > be quite useful, even just the -c form.
> >
> > Here it is:
> >
> > With unmaskirq=1 first:
> >
> >
> > 49 handle_IRQ_event 0.5104
> > 239 file_read_actor 2.4896
> > 3324 default_idle 69.2500
> > 20097 ide_output_data 104.6719
> Hey, what is this?
> Comment of the function is:
> "This is used for most PIO data transfers *to* the IDE interface"
> (see /drivers/ide/ide.c:426)
> Has it reverted to PIO mode?

This is because there are not a proper and correct state diagram data
handler set for ATAPI, period. Initially the driver evolved out of PIO
calls to the PACKET_COMMAND opcode for the ATA command set. Since there
has been zero updates/attempts to create a proper ATAPI/ASPI by anyone,
you can expect PIO transactions.

Who knows once I finally have taskfile completed and the kernel fixed to
not violate the basics of hardware atomic for storage devices, I may fix
all of the atapi/aspi transport. It is a real mess to grunt through all
the docs. However, I suspect I could get some help (co-author a
standard's proposal) with the original author to outline and create a 500+
page techincal referrence guide. So if there are any companies want to
fund such an adventure, please let me know off-line.

Understand that only in PIO can you be sure of how much data you could get
from a device, argh it still s a pig in a poke.


Andre Hedrick
LAD Storage Consulting Group

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