Re: [Qemu-devel] [PATCH 0/7] virtio: virtio-blk data plane

[Stefan Hajnoczi]

On Wed, Nov 21, 2012 at 7:42 AM, Asias He <address@hidden> wrote:
> On 11/21/2012 01:39 PM, Asias He wrote:
>> On 11/20/2012 08:25 PM, Stefan Hajnoczi wrote:
>>> On Tue, Nov 20, 2012 at 1:21 PM, Stefan Hajnoczi <address@hidden> wrote:
>>>> On Tue, Nov 20, 2012 at 10:02 AM, Asias He <address@hidden> wrote:
>>>>> Hello Stefan,
>>>>>
>>>>> On 11/15/2012 11:18 PM, Stefan Hajnoczi wrote:
>>>>>> This series adds the -device virtio-blk-pci,x-data-plane=on property that
>>>>>> enables a high performance I/O codepath.  A dedicated thread is used to 
>>>>>> process
>>>>>> virtio-blk requests outside the global mutex and without going through 
>>>>>> the QEMU
>>>>>> block layer.
>>>>>>
>>>>>> Khoa Huynh <address@hidden> reported an increase from 140,000 IOPS to 
>>>>>> 600,000
>>>>>> IOPS for a single VM using virtio-blk-data-plane in July:
>>>>>>
>>>>>>   http://comments.gmane.org/gmane.comp.emulators.kvm.devel/94580
>>>>>>
>>>>>> The virtio-blk-data-plane approach was originally presented at Linux 
>>>>>> Plumbers
>>>>>> Conference 2010.  The following slides contain a brief overview:
>>>>>>
>>>>>>   
>>>>>> http://linuxplumbersconf.org/2010/ocw/system/presentations/651/original/Optimizing_the_QEMU_Storage_Stack.pdf
>>>>>>
>>>>>> The basic approach is:
>>>>>> 1. Each virtio-blk device has a thread dedicated to handling ioeventfd
>>>>>>    signalling when the guest kicks the virtqueue.
>>>>>> 2. Requests are processed without going through the QEMU block layer 
>>>>>> using
>>>>>>    Linux AIO directly.
>>>>>> 3. Completion interrupts are injected via irqfd from the dedicated 
>>>>>> thread.
>>>>>>
>>>>>> To try it out:
>>>>>>
>>>>>>   qemu -drive if=none,id=drive0,cache=none,aio=native,format=raw,file=...
>>>>>>        -device virtio-blk-pci,drive=drive0,scsi=off,x-data-plane=on
>>>>>
>>>>>
>>>>> Is this the latest dataplane bits:
>>>>> (git://github.com/stefanha/qemu.git virtio-blk-data-plane)
>>>>>
>>>>> commit 7872075c24fa01c925d4f41faa9d04ce69bf5328
>>>>> Author: Stefan Hajnoczi <address@hidden>
>>>>> Date:   Wed Nov 14 15:45:38 2012 +0100
>>>>>
>>>>>     virtio-blk: add x-data-plane=on|off performance feature
>>>>>
>>>>>
>>>>> With this commit on a ramdisk based box, I am seeing about 10K IOPS with
>>>>> x-data-plane on and 90K IOPS with x-data-plane off.
>>>>>
>>>>> Any ideas?
>>>>>
>>>>> Command line I used:
>>>>>
>>>>> IMG=/dev/ram0
>>>>> x86_64-softmmu/qemu-system-x86_64 \
>>>>> -drive file=/root/img/sid.img,if=ide \
>>>>> -drive file=${IMG},if=none,cache=none,aio=native,id=disk1 -device
>>>>> virtio-blk-pci,x-data-plane=off,drive=disk1,scsi=off \
>>>>> -kernel $KERNEL -append "root=/dev/sdb1 console=tty0" \
>>>>> -L /tmp/qemu-dataplane/share/qemu/ -nographic -vnc :0 -enable-kvm -m
>>>>> 2048 -smp 4 -cpu qemu64,+x2apic -M pc
>>>>
>>>> Was just about to send out the latest patch series which addresses
>>>> review comments, so I have tested the latest code
>>>> (61b70fef489ce51ecd18d69afb9622c110b9315c).
>>>
>>> Rebased onto qemu.git/master before sending out.  The commit ID is now:
>>> cf6ed6406543ecc43895012a9ac9665e3753d5e8
>>>
>>> https://github.com/stefanha/qemu/commits/virtio-blk-data-plane
>>>
>>> Stefan
>>
>> Ok, thanks. /me trying
>
> Hi Stefan,
>
> If I enable the merge in guest the IOPS for seq read/write goes up to
> ~400K/300K. If I disable the merge in guest the IOPS drops to ~17K/24K
> for seq read/write (which is similar to the result I posted yesterday,
> with merge disalbed). Could you please also share the numbers for rand
> read and write in your setup?

Thanks for running the test.  Please send your rand read/write fio
jobfile so I can run the exact same test.

BTW I was running the default F18 (host) and RHEL 6.3 (guest) I/O
schedulers in my test yesterday.

Stefan