[Xen-devel] qemu VS tapdisk2 VS blkback benchmarks

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

Hi all,
as promised I run some simple benchmarks using tapdisk2 and the new qemu
as disk backends.
If you are in a hurry skip to the last section to see the test results.



SOFTWARE REQUIREMENTS
---------------------
In order to reproduce these results you need to use the new qemu with
linux aio and O_DIRECT as disk backend:

- apply the libxl patches that Anthony sent to the list a little while ago;

- compile qemu with linux aio support, you might need few hacks to work
around limitations of the glic/libaio installed in your system;

- add BDRV_O_NOCACHE|BDRV_O_NATIVE_AIO to the flags used by qemu to open
the disks;

- some gntdev fixes to allow aio and O_DIRECT on granted pages, not yet
sent to the list (but soon).




TEST HARDWARE
-------------
I am using a not so new testbox with a 64bit 2.6.37 dom0 with 752MB of ram.
The guest is a 64 bit PV Lenny guest with a 2.6.37 upstream kernel and 512MB of 
ram.
Other info about the host follows:

kontiki:~# cat /proc/cpuinfo 
processor       : 0
vendor_id       : GenuineIntel
cpu family      : 15
model           : 6
model name      : Genuine Intel(R) CPU 3.00GHz
stepping        : 2
cpu MHz         : 3000.014
cache size      : 2048 KB
fpu             : yes
fpu_exception   : yes
cpuid level     : 6
wp              : yes
flags           : fpu de tsc msr pae mce cx8 apic sep mtrr mca cmov pat clflush 
acpi mmx fxsr sse sse2 ss ht syscall nx lm constant_tsc pni est cid cx16 
hypervisor lahf_lm arat
bogomips        : 6000.02
clflush size    : 64
cache_alignment : 128
address sizes   : 36 bits physical, 48 bits virtual
power management:

processor       : 1
vendor_id       : GenuineIntel
cpu family      : 15
model           : 6
model name      : Genuine Intel(R) CPU 3.00GHz
stepping        : 2
cpu MHz         : 3000.014
cache size      : 2048 KB
fpu             : yes
fpu_exception   : yes
cpuid level     : 6
wp              : yes
flags           : fpu de tsc msr pae mce cx8 apic sep mtrr mca cmov pat clflush 
acpi mmx fxsr sse sse2 ss ht syscall nx lm constant_tsc pni est cid cx16 
hypervisor lahf_lm arat
bogomips        : 6000.02
clflush size    : 64
cache_alignment : 128
address sizes   : 36 bits physical, 48 bits virtual
power management:


kontiki:~# smartctl -a /dev/sda
Model Family:     Hitachi Deskstar T7K250 series
Device Model:     HDT722516DLA380
Serial Number:    VDN71BTCDDVR6G
Firmware Version: V43OA91A
User Capacity:    164,696,555,520 bytes
Device is:        In smartctl database [for details use: -P show]
ATA Version is:   7
ATA Standard is:  ATA/ATAPI-7 T13 1532D revision 1
Local Time is:    Fri Dec 10 16:07:57 2010 GMT
SMART support is: Available - device has SMART capability.
SMART support is: Enabled






TEST RESULTS
------------
The test is simple: write 1GB of data to disk and measure bandwidth
and cpu usage.

- tapdisk2 on raw file
bandwidth: 32MB/s
average cpu usage: 22%

- qemu on raw file
bandwidth: 33MB/s
average cpu usage: 12%

- blkback on LVM
bandwidth: 39MB/s

- qemu on LVM
bandwidth: 38MB/s




CONCLUSIONS
-----------
Qemu beats tapdisk2 on raw files (the bandwidth is the same but the cpu
usage is lower).
Qemu has similar performances to blkback on LVM from the bandwidth
perspective, but I didn't measure the cpu usage in that case.


Cheers,

Stefano

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