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Hi,

I have been doing some diskIO bench-marking of dom0 and domU (HVM). I ran into an issue where domU

performed better than dom0. So I ran few experiments to check if it is just diskIO performance.

I have an archlinux (kernel 3.5.0) + xen 4.2.2) installed on a Intel Core i7 Q720 machine. I have also installed

archlinux (kernel 3.5.0) in domU running on this machine. The domU runs with 8 vcpus. I have alloted both dom0

and domu 4096M ram.

I performed following experiments to compare the performance of domU vs dom0.

experiment 1]

1. Created a file.img of 5G

2. Mounted the file with ext2 filesystem.

3. Ran sysbench with following command.

sysbench --num-threads=8 --test=fileio --file-total-size=1G --max-requests=1000000 prepare

4. Read files into memory

script to read files

<snip>

for i in `ls test_file.*`

sudo dd if=./$i of=/dev/zero

done

</snip>

5. Ran sysbench.

sysbench --num-threads=8 --test=fileio --file-total-size=1G --max-requests=5000000 --file-test-mode=rndrd run

the output i got on dom0 is

Number of threads: 8

Extra file open flags: 0

128 files, 8Mb each

1Gb total file size

Block size 16Kb

Number of random requests for random IO: 5000000

Read/Write ratio for combined random IO test: 1.50

Periodic FSYNC enabled, calling fsync() each 100 requests.

Calling fsync() at the end of test, Enabled.

Using synchronous I/O mode

Doing random read test

Operations performed: 5130322 Read, 0 Write, 0 Other = 5130322 Total

Read 78.283Gb Written 0b Total transferred 78.283Gb (4.3971Gb/sec)

288165.68 Requests/sec executed

Test execution summary:

total time: 17.8034s

total number of events: 5130322

total time taken by event execution: 125.3102

per-request statistics:

min: 0.01ms

avg: 0.02ms

max: 55.55ms

approx. 95 percentile: 0.02ms

Threads fairness:

events (avg/stddev): 641290.2500/10057.89

execution time (avg/stddev): 15.6638/0.02

</output>

6. Performed same experiment on domU and result I got is

Number of threads: 8

Extra file open flags: 0

128 files, 8Mb each

1Gb total file size

Block size 16Kb

Number of random requests for random IO: 5000000

Read/Write ratio for combined random IO test: 1.50

Periodic FSYNC enabled, calling fsync() each 100 requests.

Calling fsync() at the end of test, Enabled.

Using synchronous I/O mode

Doing random read test

Operations performed: 5221490 Read, 0 Write, 0 Other = 5221490 Total

Read 79.674Gb Written 0b Total transferred 79.674Gb (5.9889Gb/sec)

392489.34 Requests/sec executed

Test execution summary:

total time: 13.3035s

total number of events: 5221490

total time taken by event execution: 98.7121

per-request statistics:

min: 0.01ms

avg: 0.02ms

max: 49.75ms

approx. 95 percentile: 0.02ms

Threads fairness:

events (avg/stddev): 652686.2500/1494.93

execution time (avg/stddev): 12.3390/0.02

</output>

I was expecting dom0 to performa better than domU, so to debug more into it I ram lm_bench microbenchmarks.

Experiment 2] bw_mem benchmark

1. ./bw_mem 1000m wr

dom0 output:

1048.58 3640.60

domU output:

1048.58 4719.32

2. ./bw_mem 1000m rd

dom0 output:

1048.58 5780.56

domU output:

1048.58 6258.32

Experiment 3] lat_syscall benchmark

1. ./lat_syscall write

dom0 output:

Simple write: 1.9659 microseconds

domU output :

Simple write: 0.4256 microseconds

2. ./lat_syscall read

dom0 output:

Simple read: 1.9399 microseconds

domU output :

Simple read: 0.3764 microseconds

3. ./lat_syscall stat

dom0 output:

Simple stat:3.9667 microseconds

domU output :

Simple stat: 1.2711 microseconds

I am not able to understand why domU has performed better than domU, when obvious guess is that dom0

should perform better than domU. I would really appreciate an help if anyone knows the reason behind this

issue.

Thank you,

Sushrut.

[Xen-devel] DomU vs Dom0 performance.