On Wed, Nov 28, 2001 at 03:40:44PM -0500, Stefan Doehla wrote: > Victor Yodaiken wrote: > > >On Tue, Nov 27, 2001 at 11:49:46AM -0500, Stefan Doehla wrote: > > > >>Wasn't one of the goals of the whole APIC architecture reducing > >>latencies??? > >> > > > >No. Consider interrupt path in a SMP Intel IA32 board > > assert-> I/O Apic -arbitration -> serial interrupt buss > > | > > processor apic > > > >You have a gain because you are not using the Pre-Cambrian era off chip > >PIC on the standard UP Intel motherboard, but you have a loss because > >of the arbitration, serial bus, and 2 levels of interrupt controller. > >So it's kind of a wash. > > > This is the same I thought (but didn't know if it's true) as there are > so many stages for the interrupts before they arrive at the right CPU. > > If one reads Microsoft papers or Novell developer guidelines - only use > the APIC model ... > > Anyway, the APIC thing runs with a higher clock and should be > programmable for smp affinity (I see there,s some code in RTL for this - > I just don't understand all the details ...). > > Does RTL update the APIC register with the priorities of the tasks?
No. We don't care about hardware priorities. > > Is it therefore possible to dedicate to one cpu only one interrupt when > there's a realtime thread running on this cpu? Yes. > > Annotation: IRQ latency is 5-8 us with a non-SMP kernel. > > > >We also believe that Linux performance is declining under the weight of > >all the SMP "scaling" going on in 2.2+ and think this will be an issue > >in 2.5 - but 2.5 is another headache. > > so is 2.4.x with SMP not 'realtime'-compatible? My tests here show that a > > 2.4.x kernel is not really realtime-stable. A 2.2.19 kernel is relative > okay, but 2.4.4 SMP is good for milliseconds, not microseconds ... That seems wrong - maybe you have broken hardware. -- [rtl] --- To unsubscribe: echo "unsubscribe rtl" | mail [EMAIL PROTECTED] OR echo "unsubscribe rtl <Your_email>" | mail [EMAIL PROTECTED] -- For more information on Real-Time Linux see: http://www.rtlinux.org/
