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

[bugzilla-noreply at freebsd.org]

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

Dimitry Andric <dim at FreeBSD.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dim at FreeBSD.org

--- Comment #22 from Dimitry Andric <dim at FreeBSD.org> ---
With https://reviews.freebsd.org/D29733 applied on top of 13.0-RELEASE, running
a FreeBSD guest on Ubuntu 18.04.3 LTS, with qemu-kvm 1:2.11+dfsg-1ubuntu7.19, I
see the following difference in sysbench results:

--- sysbench-acpi-fast.txt      2021-04-28 20:40:05.529460000 +0200
+++ sysbench-kvmclock.txt       2021-04-28 20:33:52.083953000 +0200
@@ -21,28 +21,28 @@

 Done.

-Total operations: 524288 (66548.67 per second)
+Total operations: 524288 (2142666.15 per second)

-512.00 MiB transferred (64.99 MiB/sec)
+512.00 MiB transferred (2092.45 MiB/sec)


 General statistics:
-    total time:                          7.8730s
+    total time:                          0.2397s
     total number of events:              524288

 Latency (ms):
          min:                                    0.00
-         avg:                                    0.01
-         max:                                    0.85
-         95th percentile:                        0.01
-         sum:                                 2644.91
+         avg:                                    0.00
+         max:                                    0.03
+         95th percentile:                        0.00
+         sum:                                  101.93

 Threads fairness:
     events (avg/stddev):           524288.0000/0.00
-    execution time (avg/stddev):   2.6449/0.00
+    execution time (avg/stddev):   0.1019/0.00

 DEBUG: Verbose per-thread statistics:

-DEBUG:     thread #  0: min: 0.0000s  avg: 0.0000s  max: 0.0008s  events:
524288
-DEBUG:                  total time taken by event execution: 2.6449s
+DEBUG:     thread #  0: min: 0.0000s  avg: 0.0000s  max: 0.0000s  events:
524288
+DEBUG:                  total time taken by event execution: 0.1019s

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