Re: [patch] Real-Time Preemption, -RT-2.6.9-mm1-V0

[Fernando Pablo Lopez-Lezcano]

On Tue, 2004-10-26 at 10:25, Lee Revell wrote:
> On Mon, 2004-10-25 at 22:11 -0700, Fernando Pablo Lopez-Lezcano wrote:
> > On Mon, 2004-10-25 at 20:01, Lee Revell wrote: 
> > > On Mon, 2004-10-25 at 20:40 +0100, Rui Nuno Capela wrote:
> > > > OTOH, jackd -R xruns are awfully back, even thought I (re)prioritize the
> > > > relevant IRQ thread handlers to be always higher than jackd's.
> > > 
> > > Actually they should be lower, except the soundcard.  I was only able to
> > > get the xrun free behavior of T3 by setting all IRQ threads except the
> > > soundcard to SCHED_OTHER.  Especially important was setting ksoftirqd to
> > > SCHED_OTHER, this actually may have been the only one necessary.
> > > 
> > > The relative priorities of jackd and the soundcard irq do not matter as
> > > these two should never contend (aka they are never both runnable at the
> > > same time).
> > 
> > What happens when one is blessed with a laptop where everything is
> > sharing an interrupt?
> > 
> > $ cat /proc/interrupts
> >            CPU0
> >   0:    2372239          XT-PIC  timer  0/72239
> >   1:       5362          XT-PIC  i8042  0/5362
> >   2:          0          XT-PIC  cascade  0/0
> >   8:          1          XT-PIC  rtc  0/1
> >   9:     616176          XT-PIC  acpi, uhci_hcd, uhci_hcd, uhci_hcd,
> > eth0, yenta, yenta, Intel 82801CA-ICH3, radeon@PCI:1:0:0  0/16176
> > 11:         37          XT-PIC  sonypi  0/35
> > 12:      28392          XT-PIC  i8042  0/28392
> > 14:      21078          XT-PIC  ide0  0/21078
> > 15:        472          XT-PIC  ide1  0/472
> 
> Ugh, why would _anyone_ design a laptop like that?  You have 4
> perfectly good interrupts that you are not using at all.  Is it really
> cheaper to put everything on the same irq?  Does this work better under
> Windows or something?
> 
> AFAIK there is nothing you can do - any other irq that fires on 9 will
> mask out all the others until it completes.

Yes, except I did not see all these xruns running 2.4.26 + lowlat +
preempt (same machine). Things got better with 2.6.x up to, perhaps, S7,
although I would have to retest to make sure. Now they seem to be worse
than before. 

-- Fernando


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