[Bug 216759] [qemu] Memory speed significantly slower under QEMUKVM emulation according to sysbench

bugzilla-noreply at freebsd.org bugzilla-noreply at freebsd.org
Fri Feb 3 19:49:53 UTC 2017


https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=216759

            Bug ID: 216759
           Summary: [qemu] Memory speed significantly slower under QEMUKVM
                    emulation according to sysbench
           Product: Base System
           Version: 11.0-RELEASE
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: freebsd-bugs at FreeBSD.org
          Reporter: andrew at azar-a.net

FreeBSD 11-RELEASE and 10.3-RELEASE seem to run memory much slower according to
sysbench benchmarking software:

Bare Metal run:
# uname -a
FreeBSD backup 10.3-RELEASE-p11 FreeBSD 10.3-RELEASE-p11 #0: Mon Oct 24
18:49:24 UTC 2016    
root at amd64-builder.daemonology.net:/usr/obj/usr/src/sys/GENERIC  amd64
# sysbench --num-threads=1 --test=memory --memory-total-size=1G run
sysbench 0.4.12:  multi-threaded system evaluation benchmark

Running the test with following options:
Number of threads: 1

Doing memory operations speed test
Memory block size: 1K

Memory transfer size: 1024M

Memory operations type: write
Memory scope type: global
Threads started!
Done.

Operations performed: 1048576 (2183178.34 ops/sec)

1024.00 MB transferred (2132.01 MB/sec)


Test execution summary:
    total time:                          0.4803s
    total number of events:              1048576
    total time taken by event execution: 0.3527
    per-request statistics:
         min:                                  0.00ms
         avg:                                  0.00ms
         max:                                  7.56ms
         approx.  95 percentile:               0.00ms

Threads fairness:
    events (avg/stddev):           1048576.0000/0.00
    execution time (avg/stddev):   0.3527/0.00


QEMU KVM emulation:
# uname -a
FreeBSD dev 11.0-RELEASE-p2 FreeBSD 11.0-RELEASE-p2 #0: Mon Oct 24 06:55:27 UTC
2016     root at amd64-builder.daemonology.net:/usr/obj/usr/src/sys/GENERIC  amd64
# sysbench --num-threads=1 --test=memory --memory-total-size=1G run
sysbench 0.4.12:  multi-threaded system evaluation benchmark

Running the test with following options:
Number of threads: 1

Doing memory operations speed test
Memory block size: 1K

Memory transfer size: 1024M

Memory operations type: write
Memory scope type: global
Threads started!
Done.

Operations performed: 1048576 (69497.13 ops/sec)

1024.00 MB transferred (67.87 MB/sec)


Test execution summary:
    total time:                          15.0880s
    total number of events:              1048576
    total time taken by event execution: 11.1440
    per-request statistics:
         min:                                  0.01ms
         avg:                                  0.01ms
         max:                                  7.32ms
         approx.  95 percentile:               0.00ms

Threads fairness:
    events (avg/stddev):           1048576.0000/0.00
    execution time (avg/stddev):   11.1440/0.00

For comparison
VMWARE:

# uname -a
FreeBSD ns3 10.2-RELEASE-p7 FreeBSD 10.2-RELEASE-p7 #0: Mon Nov  2 14:19:39 UTC
2015     root at amd64-builder.daemonology.net:/usr/obj/usr/src/sys/GENERIC  amd64
# sysbench --num-threads=1 --test=memory --memory-total-size=1G run
sysbench 0.4.12:  multi-threaded system evaluation benchmark

Running the test with following options:
Number of threads: 1

Doing memory operations speed test
Memory block size: 1K

Memory transfer size: 1024M

Memory operations type: write
Memory scope type: global
Threads started!
Done.

Operations performed: 1048576 (2234641.77 ops/sec)

1024.00 MB transferred (2182.27 MB/sec)


Test execution summary:
    total time:                          0.4692s
    total number of events:              1048576
    total time taken by event execution: 0.3437
    per-request statistics:
         min:                                  0.00ms
         avg:                                  0.00ms
         max:                                  0.09ms
         approx.  95 percentile:               0.00ms

Threads fairness:
    events (avg/stddev):           1048576.0000/0.00
    execution time (avg/stddev):   0.3437/0.00



This is not 11 only problem. VPSs with 10.3 tested also have the same problem.

I haven't found any info on this on the net. Might be because nobody tests the
RAM.
Sysbench itself starts up a thread and runs the allocation code. I couldn't
trace the thread though.
Maybe it is old code of sysbench.



Additional information and reports:
https://www.reddit.com/r/freebsd/comments/5rtf05/abysmal_memory_perfomance_witch_freebsd_under/

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