Re: [Qemu-devel] [question] virtio-blk performance degradationhappenedwith virito-serial

[Zhang Haoyu]

>> > > If virtio-blk and virtio-serial share an IRQ, the guest operating system 
>> > > has to check each virtqueue for activity. Maybe there is some 
>> > > inefficiency doing that.
>> > > AFAIK virtio-serial registers 64 virtqueues (on 31 ports + console) even 
>> > > if everything is unused.
>> > 
>> > That could be the case if MSI is disabled.
>> 
>> Do the windows virtio drivers enable MSIs, in their inf file?
>
>It depends on the version of the drivers, but it is a reasonable guess
>at what differs between Linux and Windows.  Haoyu, can you give us the
>output of lspci from a Linux guest?
>
I made a test with fio on rhel-6.5 guest, the same degradation happened too,  
this degradation can be reproduced on rhel6.5 guest 100%.
virtio_console module installed:
64K-write-sequence: 285 MBPS, 4380 IOPS
virtio_console module uninstalled:
64K-write-sequence: 370 MBPS, 5670 IOPS

And, virio-blk's interrupt mode always is MSI, no matter if virtio_console 
module is installed or uninstalled.
25:    2245933   PCI-MSI-edge      virtio1-requests

fio command:
fio -filename /dev/vda -direct=1 -iodepth=1 -thread -rw=write -ioengine=psync 
-bs=64k -size=30G -numjobs=1 -name=mytest

QEMU comamnd:
/usr/bin/kvm -id 5497356709352 -chardev 
socket,id=qmp,path=/var/run/qemu-server/5497356709352.qmp,server,nowait -mon 
chardev=qmp,mode=control -vnc :0,websocket,to=200 -enable-kvm -pidfile 
/var/run/qemu-server/5497356709352.pid -daemonize -name io-test-rhel-6.5 -smp 
sockets=1,cores=1 -cpu core2duo -nodefaults -vga cirrus -no-hpet -k en-us -boot 
menu=on,splash-time=8000 -m 4096 -usb -drive 
file=/sf/data/local/zhanghaoyu/rhel-server-6.5-x86_64-dvd.iso,if=none,id=drive-ide0,media=cdrom,aio=native,forecast=disable
 -device ide-cd,bus=ide.0,unit=0,drive=drive-ide0,id=ide0,bootindex=200 -drive 
file=/sf/data/local/images/host-1051721dff13/io-test-rhel-6.5.vm/vm-disk-1.qcow2,if=none,id=drive-virtio1,cache=none,aio=native
 -device virtio-blk-pci,drive=drive-virtio1,id=virtio1,bus=pci.0,addr=0xb 
-drive 
file=/sf/data/local/images/host-1051721dff13/io-test-rhel-6.5.vm/vm-disk-2.qcow2,if=none,id=drive-virtio2,cache=none,aio=native
 -device virtio-blk-pci,drive=drive-virtio2,id=virtio2,bus=pci
 .0,addr=0xc,bootindex=101 -netdev 
type=tap,id=net0,ifname=164922379979200,script=/sf/etc/kvm/vtp-bridge,vhost=on,vhostforce=on
 -device 
virtio-net-pci,mac=FE:FC:FE:C6:47:F6,netdev=net0,bus=pci.0,addr=0x12,id=net0,bootindex=300
 -rtc driftfix=slew,clock=rt -global kvm-pit.lost_tick_policy=discard -global 
PIIX4_PM.disable_s3=1 -global PIIX4_PM.disable_s4=1 -chardev 
socket,path=/run/virtser/1649223799792.sock,server,nowait,id=channelser -device 
virtio-serial,vectors=4 -device 
virtserialport,chardev=channelser,name=channelser.virtserial0.0

[environment]
Host:linux-3.10(RHEL7-rc1)
QEMU: qemu-2.0.1
Guest: RHEL6.5

# lspci -tv
-[0000:00]-+-00.0  Intel Corporation 440FX - 82441FX PMC [Natoma]
           +-01.0  Intel Corporation 82371SB PIIX3 ISA [Natoma/Triton II]
           +-01.1  Intel Corporation 82371SB PIIX3 IDE [Natoma/Triton II]
           +-01.2  Intel Corporation 82371SB PIIX3 USB [Natoma/Triton II]
           +-01.3  Intel Corporation 82371AB/EB/MB PIIX4 ACPI
           +-02.0  Cirrus Logic GD 5446
           +-03.0  Red Hat, Inc Virtio console
           +-0b.0  Red Hat, Inc Virtio block device
           +-0c.0  Red Hat, Inc Virtio block device
           \-12.0  Red Hat, Inc Virtio network device

# lspci -vvv
00:00.0 Host bridge: Intel Corporation 440FX - 82441FX PMC [Natoma] (rev 02)
        Subsystem: Red Hat, Inc Qemu virtual machine
        Control: I/O+ Mem+ BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- 
Stepping- SERR+ FastB2B- DisINTx-
        Status: Cap- 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- 
<MAbort- >SERR- <PERR- INTx-

00:01.0 ISA bridge: Intel Corporation 82371SB PIIX3 ISA [Natoma/Triton II]
        Subsystem: Red Hat, Inc Qemu virtual machine
        Control: I/O+ Mem+ BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- 
Stepping- SERR+ FastB2B- DisINTx-
        Status: Cap- 66MHz- UDF- FastB2B- ParErr- DEVSEL=medium >TAbort- 
<TAbort- <MAbort- >SERR- <PERR- INTx-

00:01.1 IDE interface: Intel Corporation 82371SB PIIX3 IDE [Natoma/Triton II] 
(prog-if 80 [Master])
        Subsystem: Red Hat, Inc Qemu virtual machine
        Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- 
Stepping- SERR+ FastB2B- DisINTx-
        Status: Cap- 66MHz- UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- 
<TAbort- <MAbort- >SERR- <PERR- INTx-
        Latency: 0
        Region 0: [virtual] Memory at 000001f0 (32-bit, non-prefetchable) 
[size=8]
        Region 1: [virtual] Memory at 000003f0 (type 3, non-prefetchable)
        Region 2: [virtual] Memory at 00000170 (32-bit, non-prefetchable) 
[size=8]
        Region 3: [virtual] Memory at 00000370 (type 3, non-prefetchable)
        Region 4: I/O ports at c0e0 [size=16]
        Kernel driver in use: ata_piix
        Kernel modules: ata_generic, pata_acpi, ata_piix

00:01.2 USB controller: Intel Corporation 82371SB PIIX3 USB [Natoma/Triton II] 
(rev 01) (prog-if 00 [UHCI])
        Subsystem: Red Hat, Inc Qemu virtual machine
        Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- 
Stepping- SERR+ FastB2B- DisINTx-
        Status: Cap- 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- 
<MAbort- >SERR- <PERR- INTx-
        Latency: 0
        Interrupt: pin D routed to IRQ 11
        Region 4: I/O ports at c080 [size=32]
        Kernel driver in use: uhci_hcd

00:01.3 Bridge: Intel Corporation 82371AB/EB/MB PIIX4 ACPI (rev 03)
        Subsystem: Red Hat, Inc Qemu virtual machine
        Control: I/O+ Mem+ BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- 
Stepping- SERR+ FastB2B- DisINTx-
        Status: Cap- 66MHz- UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- 
<TAbort- <MAbort- >SERR- <PERR- INTx-
        Interrupt: pin A routed to IRQ 9
        Kernel driver in use: piix4_smbus
        Kernel modules: i2c-piix4

00:02.0 VGA compatible controller: Cirrus Logic GD 5446 (prog-if 00 [VGA 
controller])
        Subsystem: Red Hat, Inc Device 1100
        Control: I/O+ Mem+ BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- 
Stepping- SERR+ FastB2B- DisINTx-
        Status: Cap- 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- 
<MAbort- >SERR- <PERR- INTx-
        Region 0: Memory at fc000000 (32-bit, prefetchable) [size=32M]
        Region 1: Memory at febd0000 (32-bit, non-prefetchable) [size=4K]
        Expansion ROM at febc0000 [disabled] [size=64K]
        Kernel modules: cirrusfb

00:03.0 Communication controller: Red Hat, Inc Virtio console
        Subsystem: Red Hat, Inc Device 0003
        Physical Slot: 3
        Control: I/O+ Mem+ BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- 
Stepping- SERR+ FastB2B- DisINTx-
        Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- 
<MAbort- >SERR- <PERR- INTx-
        Interrupt: pin A routed to IRQ 10
        Region 0: I/O ports at c0a0 [size=32]
        Region 1: Memory at febd1000 (32-bit, non-prefetchable) [size=4K]
        Capabilities: [40] MSI-X: Enable- Count=4 Masked-
                Vector table: BAR=1 offset=00000000
                PBA: BAR=1 offset=00000800
        Kernel driver in use: virtio-pci
        Kernel modules: virtio_pci

00:0b.0 SCSI storage controller: Red Hat, Inc Virtio block device
        Subsystem: Red Hat, Inc Device 0002
        Physical Slot: 11
        Control: I/O+ Mem+ BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- 
Stepping- SERR+ FastB2B- DisINTx+
        Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- 
<MAbort- >SERR- <PERR- INTx-
        Interrupt: pin A routed to IRQ 10
        Region 0: I/O ports at c000 [size=64]
        Region 1: Memory at febd2000 (32-bit, non-prefetchable) [size=4K]
        Capabilities: [40] MSI-X: Enable+ Count=2 Masked-
                Vector table: BAR=1 offset=00000000
                PBA: BAR=1 offset=00000800
        Kernel driver in use: virtio-pci
        Kernel modules: virtio_pci

00:0c.0 SCSI storage controller: Red Hat, Inc Virtio block device
        Subsystem: Red Hat, Inc Device 0002
        Physical Slot: 12
        Control: I/O+ Mem+ BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- 
Stepping- SERR+ FastB2B- DisINTx+
        Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- 
<MAbort- >SERR- <PERR- INTx-
        Interrupt: pin A routed to IRQ 11
        Region 0: I/O ports at c040 [size=64]
        Region 1: Memory at febd3000 (32-bit, non-prefetchable) [size=4K]
        Capabilities: [40] MSI-X: Enable+ Count=2 Masked-
                Vector table: BAR=1 offset=00000000
                PBA: BAR=1 offset=00000800
        Kernel driver in use: virtio-pci
        Kernel modules: virtio_pci

00:12.0 Ethernet controller: Red Hat, Inc Virtio network device
        Subsystem: Red Hat, Inc Device 0001
        Physical Slot: 18
        Control: I/O+ Mem+ BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- 
Stepping- SERR+ FastB2B- DisINTx+
        Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- 
<MAbort- >SERR- <PERR- INTx-
        Interrupt: pin A routed to IRQ 10
        Region 0: I/O ports at c0c0 [size=32]
        Region 1: Memory at febd4000 (32-bit, non-prefetchable) [size=4K]
        Expansion ROM at feb80000 [disabled] [size=256K]
        Capabilities: [40] MSI-X: Enable+ Count=3 Masked-
                Vector table: BAR=1 offset=00000000
                PBA: BAR=1 offset=00000800
        Kernel driver in use: virtio-pci
        Kernel modules: virtio_pci

Thanks,
Zhang Haoyu

>Paolo