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SubjectRe: IDE tape and SMP
On Mon, 26 Oct 1998, Gadi Oxman wrote:

> DSC overlap and ATAPI overlap are two different protocols.
>
> The above bit is set when the tape drive supports ATAPI overlap, which
> is defined as optional in QIC-157 and not currently supported by the
> Linux IDE driver. However, DSC overlap is defined as mandatory in QIC-157
> regardless of the above bit.
>
> DSC overlap greatly improves performance, as it is used by Linux to
> allow access to the tape drive and the other IDE device on the same
> channel simultaneously.
>
> Automatic disabling of DSC overlap is not a correct solution for the
> ide-tape and SMP problems, as DSC overlap in theory is not related
> at all to SMP, works correctly without SMP, and has worked all the time
> on 2.0.x (both UP and SMP) on all the drives which currently show problems
> under 2.1.x SMP.
>
> One point in which the ide-tape driver is not SMP safe, for example,
> is in code sequences such as:
>
> save_flags(flags);
> cli();
> idetape_wait_for_request();
> restore_flags(flags);
>
> However, when local interrupts are already disabled prior to cli(),
> __global_cli() doesn't seem to get the kernel lock under i386 SMP, and
> nothing seems to prevent the other processor from getting an interrupt
> and servicing the request which we intended to wait on before we even
> installed a semaphore in it and used down().

Gadi,

I know that you wrote the original source, and we both know that I am
trying to play pick and learn in weeks and months what you did in years.
The reality is that it will be a long time before I can move through the
source like you and Mark can. So what will it take to get you to pick up
an play again?

Second, I will follow your suggested direction. As always, you will be
needed to point out assumption follies until more knowledge is hammered
into my skull.

Just by chance, would you send me copies of any and all
docs/whitepages/etc and or forward the locations where I can get them??
I have piles of stuff already and my wife wants me to stop the piles, but
to quote a silly movie......"MORE INPUT, MORE INPUT"........


Cheers,
Andre Hedrick
The IDE-FNG for Linux
The APC UPS Specialist for Linux

http://www.dyer.vanderbilt.edu/server/udma/
http://www.dyer.vanderbilt.edu/server/apcupsd/ BINARIES


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