[Users] RE: slow fsync rate

Martin Maurer martin at proxmox.com
Tue Aug 24 14:53:51 EDT 2010


Hi all,



I just tested the latest OpenVZ kernel 2.6.32 (bykovsky) from today with sysbench, I just got 63.12 Requests/sec executed (see below).

2.6.18 and 2.6.24 OpenVZ Kernels performs well,   I got 1074.81 Requests/sec executed. What's wrong here, why is the 2.6.32 branch so slow regarding fsyns/sec? (I am using ext3)

____

OpenVZ 2.6.24:~# sysbench --test=fileio --file-num=1 --file-total-size=50G --file-fsync-all=on --file-test-mode=seqrewr --max-time=100 --file-block-size=4096 --max-requests=0 run

sysbench 0.4.12:  multi-threaded system evaluation benchmark



Running the test with following options:

Number of threads: 1



Extra file open flags: 0

1 files, 50Gb each

50Gb total file size

Block size 4Kb

Calling fsync() after each write operation.

Using synchronous I/O mode

Doing sequential rewrite test

Threads started!

Time limit exceeded, exiting...

Done.



Operations performed:  0 Read, 107485 Write, 107485 Other = 214970 Total

Read 0b  Written 419.86Mb  Total transferred 419.86Mb  (4.1985Mb/sec)

1074.81 Requests/sec executed



Test execution summary:

    total time:                          100.0033s

    total number of events:              107485

    total time taken by event execution: 99.9460

    per-request statistics:

         min:                                  0.54ms

         avg:                                  0.93ms

         max:                                 97.34ms

         approx.  95 percentile:               0.87ms



Threads fairness:

    events (avg/stddev):           107485.0000/0.00

    execution time (avg/stddev):   99.9460/0.00



_____





Testing newest Kernel: 2.6.32-bykovsky.1 #1 SMP Mon Aug 23 19:59:54 MSD 2010 x86_64



I just got 63.12 Requests/sec executed. Here are the details, can someone reproduce this?

_____

OpenVZ 2.6.32:~#  sysbench --test=fileio --file-num=1 --file-total-size=50G --file-fsync-all=on --file-test-mode=seqrewr --max-time=100 --file-block-size=4096 --max-requests=0 run



sysbench 0.4.12:  multi-threaded system evaluation benchmark



Running the test with following options:

Number of threads: 1



Extra file open flags: 0

1 files, 50Gb each

50Gb total file size

Block size 4Kb

Calling fsync() after each write operation.

Using synchronous I/O mode

Doing sequential rewrite test

Threads started!

Time limit exceeded, exiting...

Done.



Operations performed:  0 Read, 6312 Write, 6312 Other = 12624 Total

Read 0b  Written 24.656Mb  Total transferred 24.656Mb  (252.46Kb/sec)

   63.12 Requests/sec executed



Test execution summary:

    total time:                          100.0070s

    total number of events:              6312

    total time taken by event execution: 99.9838

    per-request statistics:

         min:                                  7.70ms

         avg:                                 15.84ms

         max:                                260.40ms

         approx.  95 percentile:              16.70ms



Threads fairness:

    events (avg/stddev):           6312.0000/0.00

    execution time (avg/stddev):   99.9838/0.00

___

Br, Martin

From: users-bounces at openvz.org [mailto:users-bounces at openvz.org] On Behalf Of Dietmar Maurer
Sent: Dienstag, 24. August 2010 10:36
To: users at openvz.org
Subject: [Users] slow fsync rate

Hi all,

we observe very slow fsync rates on newer 2.6.32 kernel with OpenVZ:

It is possible to reproduce the problem with sysbench:

# sysbench --test=fileio --file-num=1 --file-total-size=50G --file-fsync-all=on --file-test-mode=seqrewr --max-time=100 --file-block-size=4096 --max-requests=0 run

Requests/sec executed is considerable slower on OpenVZ kernel (factor 20 on Intel Modular Server).

Can someone reproduce that problem?

- Dietmar


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