[Bug 216759] [kern] Memory speed with small blocks (1K) up to 35 times slower than host system (under QEMU emulation, but not only)

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

--- Comment #7 from andrew at azar-a.net ---
Same config VPS on QEMU with CentOS 7

# 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 (1491466.64 ops/sec)

1024.00 MB transferred (1456.51 MB/sec)


Test execution summary:
    total time:                          0.7031s
    total number of events:              1048576
    total time taken by event execution: 0.5486
    per-request statistics:
         min:                                  0.00ms
         avg:                                  0.00ms
         max:                                 18.49ms
         approx.  95 percentile:               0.00ms

Threads fairness:
    events (avg/stddev):           1048576.0000/0.00
    execution time (avg/stddev):   0.5486/0.00


The node running it:

# 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 (3862725.85 ops/sec)

1024.00 MB transferred (3772.19 MB/sec)


Test execution summary:
    total time:                          0.2715s
    total number of events:              1048576
    total time taken by event execution: 0.2213
    per-request statistics:
         min:                                  0.00ms
         avg:                                  0.00ms
         max:                                  0.04ms
         approx.  95 percentile:               0.00ms

Threads fairness:
    events (avg/stddev):           1048576.0000/0.00
    execution time (avg/stddev):   0.2213/0.00

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