[Users] RE: slow fsync rate

[Kirill Korotaev]

These numbers very much resemble fsync() rate with write cache enabled (~1000/sec) and disabled (50-70/sec).
check write cache settings with hdparm + check whether you have barrier mount option on ext3.

I believe, 2.6.32 is just more honest on fsync and really forces drive to save data. While earlier kernels
did this only with BARRIER mount option (or ignored this problem at all)...

Thanks,
Kirill


On Aug 24, 2010, at 22:53 , Martin Maurer wrote:

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> [mailto:users-bounces at openvz.org] On Behalf Of Dietmar Maurer
Sent: Dienstag, 24. August 2010 10:36
To: users at openvz.org<mailto: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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