Re: [Qemu-devel] slow virtio network with vhost=on and multiple cores

[Michael S. Tsirkin]

On Tue, Nov 13, 2012 at 12:49:03PM +0100, Peter Lieven wrote:
> 
> On 09.11.2012 19:03, Peter Lieven wrote:
> >Remark:
> >If i disable interrupts on CPU1-3 for virtio the performance is ok again.
> >
> >Now we need someone with deeper knowledge of the in-kernel irqchip and the
> >virtio/vhost driver development to say if this is a regression in qemu-kvm
> >or a problem with the old virtio drivers if they receive the interrupt on
> >different CPUs.
> anyone?

Looks like the problem is not in the guest: I tried ubuntu guest
on a rhel host, I got 8GB/s with vhost and 4GB/s without
on a host to guest banchmark.



> 
> >
> >Peter Lieven wrote:
> >>it seems that with in-kernel irqchip the interrupts are distributed across
> >>all vpcus. without in-kernel irqchip all interrupts are on cpu0. maybe
> >>this is related.
> >>
> >>without inkernel irqchip
> >>            CPU0       CPU1       CPU2       CPU3
> >>   0:         16          0          0          0   IO-APIC-edge      timer
> >>   1:         23          0          0          0   IO-APIC-edge      i8042
> >>   4:          1          0          0          0   IO-APIC-edge
> >>   6:          4          0          0          0   IO-APIC-edge
> >>floppy
> >>   7:          0          0          0          0   IO-APIC-edge
> >>parport0
> >>   8:          0          0          0          0   IO-APIC-edge      rtc0
> >>   9:          0          0          0          0   IO-APIC-fasteoi   acpi
> >>  11:         76          0          0          0   IO-APIC-fasteoi
> >>uhci_hcd:usb1
> >>  12:        102          0          0          0   IO-APIC-edge      i8042
> >>  14:          0          0          0          0   IO-APIC-edge
> >>ata_piix
> >>  15:      16881          0          0          0   IO-APIC-edge
> >>ata_piix
> >>  24:          0          0          0          0   PCI-MSI-edge
> >>virtio1-config
> >>  25:       5225          0          0          0   PCI-MSI-edge
> >>virtio1-requests
> >>  26:          0          0          0          0   PCI-MSI-edge
> >>virtio0-config
> >>  27:      72493          0          0          0   PCI-MSI-edge
> >>virtio0-input
> >>...
> >>
> >>with inkernel irqchip
> >>            CPU0       CPU1       CPU2       CPU3
> >>   0:         16          0          0          0   IO-APIC-edge      timer
> >>   1:          0          3          3          1   IO-APIC-edge      i8042
> >>   4:          0          0          1          0   IO-APIC-edge
> >>   6:          1          0          1          2   IO-APIC-edge
> >>floppy
> >>   7:          0          0          0          0   IO-APIC-edge
> >>parport0
> >>   8:          0          0          0          0   IO-APIC-edge      rtc0
> >>   9:          0          0          0          0   IO-APIC-fasteoi   acpi
> >>  11:          7          9          4          1   IO-APIC-fasteoi
> >>uhci_hcd:usb1
> >>  12:         30         27         29         34   IO-APIC-edge      i8042
> >>  14:          0          0          0          0   IO-APIC-edge
> >>ata_piix
> >>  15:        943        937        950        943   IO-APIC-edge
> >>ata_piix
> >>  24:          0          0          0          0   PCI-MSI-edge
> >>virtio0-config
> >>  25:        930        978        980        947   PCI-MSI-edge
> >>virtio0-input
> >>  26:          0          0          1          0   PCI-MSI-edge
> >>virtio0-output
> >>  27:          0          0          0          0   PCI-MSI-edge
> >>virtio1-config
> >>  28:        543        541        542        553   PCI-MSI-edge
> >>virtio1-requests
> >>...
> >>
> >>
> >