This serves as a performance benchmark as well as a stress test
for QHT. We can tweak quite a number of things, including the
number of resize threads and how frequently resizes are triggered.

A performance comparison of QHT vs CLHT[1] and ck_hs[2] using
this same benchmark program can be found here:
  http://imgur.com/a/0Bms4

The tests are run on a 64-core AMD Opteron 6376, pinning threads
to cores favoring same-socket cores. For each run, qht-bench is
invoked with:
  $ tests/qht-bench -d $duration -n $n -u $u -g $range
, where $duration is in seconds, $n is the number of threads,
$u is the update rate (0.0 to 100.0), and $range is the number
of keys.

Note that ck_hs's performance drops significantly as writes go
up, since it requires an external lock (I used a ck_spinlock)
around every write.

Also, note that CLHT instead of using a seqlock, relies on an
allocator that does not ever return the same address during the
same read-critical section. This gives it a slight performance
advantage over QHT on read-heavy workloads, since the seqlock
writes aren't there.

[1] CLHT: https://github.com/LPD-EPFL/CLHT
          https://infoscience.epfl.ch/record/207109/files/ascy_asplos15.pdf

[2] ck_hs: http://concurrencykit.org/
           http://backtrace.io/blog/blog/2015/03/13/workload-specialization/

A few of those plots are shown in text here, since that site
might not be online forever. Throughput is on Mops/s on the Y axis.

                             200K keys, 0 % updates

  450 ++--+------+------+-------+-------+-------+-------+------+-------+--++
      |   +      +      +       +       +       +       +      +      +N+  |
  400 ++                                                           ---+E+ ++
      |                                                       +++----      |
  350 ++          9 ++------+------++                       --+E+    -+H+ ++
      |             |      +H+-     |                 -+N+----   ---- +++  |
  300 ++          8 ++     +E+     ++             -----+E+  --+H+         ++
      |             |      +++      |         -+N+-----+H+--               |
  250 ++          7 ++------+------++  +++-----+E+----                    ++
  200 ++                    1         -+E+-----+H+                        ++
      |                           ----                     qht +-E--+      |
  150 ++                      -+E+                        clht +-H--+     ++
      |                   ----                              ck +-N--+      |
  100 ++               +E+                                                ++
      |            ----                                                    |
   50 ++       -+E+                                                       ++
      |   +E+E+  +      +       +       +       +       +      +       +   |
    0 ++--E------+------+-------+-------+-------+-------+------+-------+--++
          1      8      16      24      32      40      48     56      64
                                Number of threads

                             200K keys, 1 % updates

  350 ++--+------+------+-------+-------+-------+-------+------+-------+--++
      |   +      +      +       +       +       +       +      +     -+E+  |
  300 ++                                                         -----+H+ ++
      |                                                       +E+--        |
      |           9 ++------+------++                  +++----             |
  250 ++            |      +E+   -- |                 -+E+                ++
      |           8 ++         --  ++             ----                     |
  200 ++            |      +++-     |  +++  ---+E+                        ++
      |           7 ++------N------++ -+E+--               qht +-E--+      |
      |                     1  +++----                    clht +-H--+      |
  150 ++                      -+E+                          ck +-N--+     ++
      |                   ----                                             |
  100 ++               +E+                                                ++
      |            ----                                                    |
      |        -+E+                                                        |
   50 ++    +H+-+N+----+N+-----+N+------                                  ++
      |   +E+E+  +      +       +      +N+-----+N+-----+N+----+N+-----+N+  |
    0 ++--E------+------+-------+-------+-------+-------+------+-------+--++
          1      8      16      24      32      40      48     56      64
                                Number of threads

                             200K keys, 20 % updates

  300 ++--+------+------+-------+-------+-------+-------+------+-------+--++
      |   +      +      +       +       +       +       +      +       +   |
      |                                                              -+H+  |
  250 ++                                                         ----     ++
      |           9 ++------+------++                       --+H+  ---+E+  |
      |           8 ++     +H+--   ++                 -+H+----+E+--        |
  200 ++            |      +E+    --|             -----+E+--  +++         ++
      |           7 ++      + ---- ++       ---+H+---- +++ qht +-E--+      |
  150 ++          6 ++------N------++ -+H+-----+E+        clht +-H--+     ++
      |                     1     -----+E+--                ck +-N--+      |
      |                       -+H+----                                     |
  100 ++                  -----+E+                                        ++
      |                +E+--                                               |
      |            ----+++                                                 |
   50 ++       -+E+                                                       ++
      |     +E+ +++                                                        |
      |   +E+N+-+N+-----+       +       +       +       +      +       +   |
    0 ++--E------+------N-------N-------N-------N-------N------N-------N--++
          1      8      16      24      32      40      48     56      64
                                Number of threads

                            200K keys, 100 % updates       qht +-E--+
                                                          clht +-H--+
  160 ++--+------+------+-------+-------+-------+-------+---ck-+-N-----+--++
      |   +      +      +       +       +       +       +      +   ----H   |
  140 ++                                                      +H+--  -+E+ ++
      |                                                +++----   ----      |
  120 ++          8 ++------+------++                 -+H+    +E+         ++
      |           7 ++     +H+---- ++             ---- +++----             |
  100 ++            |      +E+      |  +++  ---+H+    -+E+                ++
      |           6 ++     +++     ++ -+H+--   +++----                     |
   80 ++          5 ++------N----------+E+-----+E+                        ++
      |                     1 -+H+---- +++                                 |
      |                   -----+E+                                         |
   60 ++               +H+---- +++                                        ++
      |            ----+E+                                                 |
   40 ++        +H+----                                                   ++
      |       --+E+                                                        |
   20 ++    +E+                                                           ++
      |  +EE+    +      +       +       +       +       +      +       +   |
    0 ++--+N-N---N------N-------N-------N-------N-------N------N-------N--++
          1      8      16      24      32      40      48     56      64
                                Number of threads
Signed-off-by: NEmilio G. Cota <cota@braap.org>
Message-Id: <1465412133-3029-13-git-send-email-cota@braap.org>
Signed-off-by: NRichard Henderson <rth@twiddle.net>