Date: Wed, 29 Nov 2000 18:28:40 -0600 From: David Kelly <dkelly@hiwaay.net> To: Terry Lambert <tlambert@primenet.com> Cc: questions@FreeBSD.ORG Subject: Re: ATAPI CD-RW drive: how? Message-ID: <200011300028.eAU0SeS59757@grumpy.dyndns.org> In-Reply-To: Message from Terry Lambert <tlambert@primenet.com> of "Wed, 29 Nov 2000 17:53:32 GMT." <200011291753.KAA18886@usr08.primenet.com>
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Terry Lambert writes:
> > > I think the lockup is starting up team and dd at rtprio 5 to
> > > keep the CDROM writer streaming, regardless of whatever else
> > > is running on the system.
> >
> > The lockup I was refering to was with cdrecord under Irix and FreeBSD,
> > without any external rtprio or dd or team or nothing. Cdrecord has to
> > run as root to access the kernel priority mechanism. And at least in
> > versions around 1.6 when the cdrecord starts on the recorder it locks
> > out everything (think under Irix 6.3 the mouse pointer would even stop,
> > but the network would still ping) at the start of the burn procedure.
>
> I can explain the mouse pointer stopping. The VM system and
> buffer cache on System V derived systems are cannibalistic;
> you will see the same lockup of your X server when linking a
> large program, if you are using the standard linker, since
> the standard linker will map all your object files, and seek
> around like a maniac.
[...]
I don't think it was that exotic. The cdrecord man page says a lot about
priority levels and real time features of kernels, that on some systems
its unable to gain higher priority than internal kernel processes, and
says this about Solaris which I don't fully understand but maybe you do:
Cdrecord runs at priority 59 on Solaris, you should run
mkisofs at no more than priority 58. On other systems, you
should run mkisofs at no less than nice --18.
Under Irix, the system froze the first time cdrecord accesses the blank
CD-R. All other disk activity stops (as observed by LEDs on the
devices). The freeze was fairly long, 10 to 15 seconds and ended when
the CD-R LED started flickering. I believe it was exactly the same under
FreeBSD 2.2.8.
Its very likely it was a timed hang with the intent of presetting VM
state.
--
David Kelly N4HHE, dkelly@hiwaay.net
=====================================================================
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