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


From: Michael S. Tsirkin
Subject: Re: [Qemu-devel] slow virtio network with vhost=on and multiple cores
Date: Tue, 13 Nov 2012 18:33:32 +0200

On Tue, Nov 13, 2012 at 06:22:56PM +0200, Michael S. Tsirkin wrote:
> 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.
> 

Tried with upstream qemu on rhel kernel and that's even a bit faster.
So it's ubuntu kernel. vanilla 2.6.32 didn't have vhost at all
so maybe their vhost backport is broken insome way.

> 
> > 
> > >
> > >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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