[lug] noapic option

[D. Stimits]

"Ian S. Nelson" wrote:
> 
> Rodger Wilson {I/O Software} wrote:
> 
> > I have been having a hell of a time latly getting a few of my scsi
> > cards working with linux.  I finally figured out that I need to boot
> > linux with the noapic option.
> >
> > This seems to make linux so that it will boot, but not stable!
> 
> Doesn't the APIC route the interrupts to the correct processor in an
> SMP system?   Turning off the APIC, whatever that may mean, may have
> fundamental problems with SMP.

This is what it does for Intel SMP chipsets. SMP will work fine without
it, but it degrades performance badly. Hardware devices require irq
handling, and with no apic, all hardware must be serviced by cpu#0. The
responsiveness of SMP under load has always been far better than a
single cpu of twice the speed, which is a big reason to go with SMP (for
smooth response under load, versus speed). This advantage is gone
without apic, but threaded programs still benefit completely. So long as
you don't require hardware access with a piece of software, it won't
know the difference.

> 
> > I am guessing that this does something with the Priority Interupt
> > Controler.  Does anyone know what the real issue that the noapic
> > options really deals with, and/or other ways to really fix the
> > problemr?
> 
> Does it crash  in uniprocessor mode?
> 
> Which kernel is this running?
> 
> --
> Ian S. Nelson                                           __o
> Nelson_ at attglobal.net.NOSPAM                            \<,
>                                                       ()/ ()
> 
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