Re: [Xen-devel] DomU vs Dom0 performance.

[sushrut shirole <shirole.sushrut@xxxxxxxxx>]

Hi,

I am using qemu device model. 

Disk configuration line is :

disk = [ 'phy:/dev/sda5,hda,w', 'file:/root/dev/iso/archlinux.iso,hdc:cdrom,r' ]

boot="c"

--

Thanks

On 30 September 2013 14:50, Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx> wrote:

On Sun, 29 Sep 2013, sushrut shirole wrote:
> 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.

What kind of disk backend are you using? QEMU or blkback?
Could you please post your disk line from your VM config file?

> 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.*`
> do
>    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
>
> <output>
> 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
>
> <output>
> 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.
>
>
>

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