On Apr 21, 2009, at 10:56 AM, Subodh Nijsure wrote:
Hi,
I have board with MPC8572E (dual core PPC). I have one board running
kernel
with IRQ_ALL_CPUS set to Y and another with that option turned off.
Kernel
version #2.6.26
With IRQ_ALL_CPUS turned off
( Here interrupts all go to CPU0 )
hdparm -tT /dev/hda
/dev/hda:
Timing cached reads: 3048 MB in 2.00 seconds = 1523.79 MB/sec
Timing buffered disk reads: 10 MB in 3.07 seconds = 3.25 MB/sec
cat /proc/interrupts
CPU0 CPU1
18: 1394100 0 OpenPIC Edge ide0
With IRQ_ALL_CPUS turned on I see
(Here interrupts go to CPU0 and CPU1 )
hdparm -tT /dev/hda
/dev/hda:
Timing cached reads: 1076 MB in 2.00 seconds = 538.01 MB/sec
Timing buffered disk reads: 10 MB in 3.08 seconds = 3.25 MB/sec
cat /proc/interrupts
CPU0 CPU1
18: 44951 54765 OpenPIC Edge ide0
I "expected" that with IRQ_ALL_CPUS -- interrupt sharing I would be
able to
get higher througput but I see things otherway around.
Would someone care to enlighten me as to why when I set IRQ_ALL_CPUS
disk
I/O performance goes down so much? Under what circumstances should
one then
turn on IRQ_ALL_CPUS option on PPC platform?
Regards,
/Subodh
This is probably because you are getting ill defined behavior on
8572. The 8572 (and any FSL MPIC) doesn't actually support having the
PIC distribute interrupts to the different CPUs. Its technically
"illegal" to set more than one destination processor.
If you want to try and distribute interrupts than I suggest looking at
irqbalance.
I'll look at a patch to deal with IRQ_ALL_CPUS to not setup the insane
HW scenario.
- k
_______________________________________________
Linuxppc-dev mailing list
Linuxppc-dev@ozlabs.org
https://ozlabs.org/mailman/listinfo/linuxppc-dev
