[svlug] shufflin'around interrupts in software

Florin Andrei florin at sgi.com
Fri Jan 10 11:06:58 PST 2003


On Thu, 2003-01-09 at 14:13, Florin Andrei wrote:
> 
> http://www.msicomputer.com/product/detail_spec/product_detail.asp?model=K7N420_Pro
> - AthlonXP 1800+ CPU
> - Red Hat 8.0 fully updated (over a RH Network subscription)
> - updated RH Athlon kernels
> it's fairly ok even for 3D), when i play various video formats, every 10
> seconds or so (very irregularly) the image makes a small (sub-second)
> jerk or two; at the same moment, if i look in the CPU usage history,
> there's a momentary (sub-second) increase in the CPU usage.
> I've been told that the problem may be caused by overlaping interrupts,

I might have made some progress. For whatever reason, APIC is not
enabled on my system. No wonder the IRQs are so crowded.
I tried to enable APIC, but failed. I tried to pass different parameters
to the kernel: "apic", "pirq=0", etc. I tried to play with BIOS options
but nothing worked so far.
Strange thing is, someone i know has the same type of motherboard (MSI
nForce) and he has APIC enabled just fine (and he didn't do anything to
get it working).

Are you guys aware of APIC-related problems with Athlon systems? Or with
Red Hat kernels? Or a combination of these?
I may do some tests with vanilla 2.4 kernels, and possibly another test
using the Con Kolivas patch (it's a mega-patch: includes O(1), low-lat,
preempt and optionally AA VM, 1000Hz and stuff like that).

As a workaround, meanwhile i killed LPT and COM from the BIOS (i wasn't
using them anyway), so that i got more room for the IRQs. The system
_appears_ to work somewhat better, but i need to do more testing.
But that won't work anymore once i'll get the new IDE controller card,
and possibly a SCSI controller too, because those things will eat up
more IRQs.

New interrupt table (looks much better for now):

#############################
[florin at rivendell florin]$ cat /proc/interrupts
           CPU0
  0:   19416206          XT-PIC  timer
  1:       1388          XT-PIC  keyboard
  2:          0          XT-PIC  cascade
  3:          0          XT-PIC  usb-ohci
  4:          1          XT-PIC  ohci1394
  7:          1          XT-PIC  usb-ohci, NVidia NForce
  8:          1          XT-PIC  rtc
 10:    3233238          XT-PIC  nvidia
 11:    9982385          XT-PIC  eth0
 12:     162113          XT-PIC  PS/2 Mouse
 14:      85464          XT-PIC  ide0
 15:     755831          XT-PIC  ide1
NMI:          0
ERR:          1
[florin at rivendell florin]$
#############################

-- 
Florin Andrei

"Were any orcs or 'dark men' offered coalition positions
in King Aragorn's cabinet, at the end of the War of the Ring?
Was Mordor given a benign Marshall Plan?" - David Brin




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