Radim,
Thanks for your answer. Indeed setting IRQ affinity to a specific core
seems to be respected.
However, on software emulation and on the real machine, while IRQ
affinity defaults to 3, all interrupts go on CPU0, while on KVM they go
on CPU1.
I wonder why KVM would act differently than both the real machine and
the software emulation in this particular aspect.
Is there a machine or processor that I can specify at KVM command line
to make it behave like the real x86_64 processor which defaults
interrupts to CPU0?
Thanks,
Mihai
On 08/21/2015 02:20 AM, Radim Krčmář wrote:
2015-08-20 17:16+0300, Mihai Neagu:
Here is how IRQ affinity is configured on guest at startup, in an init.d
script:
echo 1 > /proc/irq/default_smp_affinity
for x in /proc/irq/*/smp_affinity;
do
echo 1 > $x
done 2> /dev/null
The command line for starting the hardware accelerated VM:
qemu-system-x86-64 -enable-kvm -kernel bzImage -hda rootfs.ext2 -append \
"root=/dev/sda console=ttyS0 rw" -nographic -cpu qemu64 -snapshot -smp 2 \
-m 2048
On the hardware accelerated guest, 'cat /proc/interrupts' shows:
CPU0 CPU1
0: 26 0 IO-APIC-edge timer
1: 7 4 IO-APIC-edge i8042
4: 1137 523 IO-APIC-edge serial
8: 0 1 IO-APIC-edge rtc0
9: 0 0 IO-APIC-fasteoi acpi
11: 4971 4 IO-APIC-fasteoi eth0
12: 66 64 IO-APIC-edge i8042
14: 1958 714 IO-APIC-edge ata_piix
15: 4512 63 IO-APIC-edge ata_piix
...
Interrupts are serviced on both cores, even though affinity is set to 1.
KVM's APIC balances interrupts -- until you set the affinity (probably
near the end of boot process), both CPUs are going to receive roughly
the same amount but after directing subsequent interrupts to CPU0, CPU1
shouldn't receive more.
Please verify that CPU0 is not receiving all interrupts by doing a
difference between two `cat /proc/interrupts` after the affinity was
set. (CPU0 has higher numbers in your excerpt, which makes me suspect
that it works as expected.)
Thanks.
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