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


From: Peter Lieven
Subject: Re: [Qemu-devel] slow virtio network with vhost=on and multiple cores
Date: Tue, 13 Nov 2012 12:49:03 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:16.0) Gecko/20121028 Thunderbird/16.0.2


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?



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
...







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