perf bench: Use condition variables in numa.

The existing approach to synchronization between threads in the numa
benchmark is unbalanced mutexes.

This synchronization causes thread sanitizer to warn of locks being
taken twice on a thread without an unlock, as well as unlocks with no
corresponding locks.

This change replaces the synchronization with more regular condition
variables.

While this fixes one class of thread sanitizer warnings, there still
remain warnings of data races due to threads reading and writing shared
memory without any atomics.

Committer testing:

  Basic run on a non-NUMA machine.

  # perf bench numa

          # List of available benchmarks for collection 'numa':

             mem: Benchmark for NUMA workloads
             all: Run all NUMA benchmarks

  # perf bench numa all
  # Running numa/mem benchmark...

   # Running main, "perf bench numa numa-mem"
   #
   # Running test on: Linux five 5.8.12-200.fc32.x86_64 #1 SMP Mon Sep 28 12:17:31 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
   #

   # Running RAM-bw-local, "perf bench numa mem -p 1 -t 1 -P 1024 -C 0 -M 0 -s 20 -zZq --thp  1 --no-data_rand_walk"
           20.076 secs slowest (max) thread-runtime
           20.000 secs fastest (min) thread-runtime
           20.073 secs average thread-runtime
            0.190 % difference between max/avg runtime
          241.828 GB data processed, per thread
          241.828 GB data processed, total
            0.083 nsecs/byte/thread runtime
           12.045 GB/sec/thread speed
           12.045 GB/sec total speed

   # Running RAM-bw-local-NOTHP, "perf bench numa mem -p 1 -t 1 -P 1024 -C 0 -M 0 -s 20 -zZq --thp  1 --no-data_rand_walk --thp -1"
           20.045 secs slowest (max) thread-runtime
           20.000 secs fastest (min) thread-runtime
           20.014 secs average thread-runtime
            0.111 % difference between max/avg runtime
          234.304 GB data processed, per thread
          234.304 GB data processed, total
            0.086 nsecs/byte/thread runtime
           11.689 GB/sec/thread speed
           11.689 GB/sec total speed

   # Running RAM-bw-remote, "perf bench numa mem -p 1 -t 1 -P 1024 -C 0 -M 1 -s 20 -zZq --thp  1 --no-data_rand_walk"

  Test not applicable, system has only 1 nodes.

   # Running RAM-bw-local-2x, "perf bench numa mem -p 2 -t 1 -P 1024 -C 0,2 -M 0x2 -s 20 -zZq --thp  1 --no-data_rand_walk"
           20.138 secs slowest (max) thread-runtime
           20.000 secs fastest (min) thread-runtime
           20.121 secs average thread-runtime
            0.342 % difference between max/avg runtime
          135.961 GB data processed, per thread
          271.922 GB data processed, total
            0.148 nsecs/byte/thread runtime
            6.752 GB/sec/thread speed
           13.503 GB/sec total speed

   # Running RAM-bw-remote-2x, "perf bench numa mem -p 2 -t 1 -P 1024 -C 0,2 -M 1x2 -s 20 -zZq --thp  1 --no-data_rand_walk"

  Test not applicable, system has only 1 nodes.

   # Running RAM-bw-cross, "perf bench numa mem -p 2 -t 1 -P 1024 -C 0,8 -M 1,0 -s 20 -zZq --thp  1 --no-data_rand_walk"

  Test not applicable, system has only 1 nodes.

   # Running  1x3-convergence, "perf bench numa mem -p 1 -t 3 -P 512 -s 100 -zZ0qcm --thp  1"
            0.747 secs latency to NUMA-converge
            0.747 secs slowest (max) thread-runtime
            0.000 secs fastest (min) thread-runtime
            0.714 secs average thread-runtime
           50.000 % difference between max/avg runtime
            3.228 GB data processed, per thread
            9.683 GB data processed, total
            0.231 nsecs/byte/thread runtime
            4.321 GB/sec/thread speed
           12.964 GB/sec total speed

   # Running  1x4-convergence, "perf bench numa mem -p 1 -t 4 -P 512 -s 100 -zZ0qcm --thp  1"
            1.127 secs latency to NUMA-converge
            1.127 secs slowest (max) thread-runtime
            1.000 secs fastest (min) thread-runtime
            1.089 secs average thread-runtime
            5.624 % difference between max/avg runtime
            3.765 GB data processed, per thread
           15.062 GB data processed, total
            0.299 nsecs/byte/thread runtime
            3.342 GB/sec/thread speed
           13.368 GB/sec total speed

   # Running  1x6-convergence, "perf bench numa mem -p 1 -t 6 -P 1020 -s 100 -zZ0qcm --thp  1"
            1.003 secs latency to NUMA-converge
            1.003 secs slowest (max) thread-runtime
            0.000 secs fastest (min) thread-runtime
            0.889 secs average thread-runtime
           50.000 % difference between max/avg runtime
            2.141 GB data processed, per thread
           12.847 GB data processed, total
            0.469 nsecs/byte/thread runtime
            2.134 GB/sec/thread speed
           12.805 GB/sec total speed

   # Running  2x3-convergence, "perf bench numa mem -p 2 -t 3 -P 1020 -s 100 -zZ0qcm --thp  1"
            1.814 secs latency to NUMA-converge
            1.814 secs slowest (max) thread-runtime
            1.000 secs fastest (min) thread-runtime
            1.716 secs average thread-runtime
           22.440 % difference between max/avg runtime
            3.747 GB data processed, per thread
           22.483 GB data processed, total
            0.484 nsecs/byte/thread runtime
            2.065 GB/sec/thread speed
           12.393 GB/sec total speed

   # Running  3x3-convergence, "perf bench numa mem -p 3 -t 3 -P 1020 -s 100 -zZ0qcm --thp  1"
            2.065 secs latency to NUMA-converge
            2.065 secs slowest (max) thread-runtime
            1.000 secs fastest (min) thread-runtime
            1.947 secs average thread-runtime
           25.788 % difference between max/avg runtime
            2.855 GB data processed, per thread
           25.694 GB data processed, total
            0.723 nsecs/byte/thread runtime
            1.382 GB/sec/thread speed
           12.442 GB/sec total speed

   # Running  4x4-convergence, "perf bench numa mem -p 4 -t 4 -P 512 -s 100 -zZ0qcm --thp  1"
            1.912 secs latency to NUMA-converge
            1.912 secs slowest (max) thread-runtime
            1.000 secs fastest (min) thread-runtime
            1.775 secs average thread-runtime
           23.852 % difference between max/avg runtime
            1.479 GB data processed, per thread
           23.668 GB data processed, total
            1.293 nsecs/byte/thread runtime
            0.774 GB/sec/thread speed
           12.378 GB/sec total speed

   # Running  4x4-convergence-NOTHP, "perf bench numa mem -p 4 -t 4 -P 512 -s 100 -zZ0qcm --thp  1 --thp -1"
            1.783 secs latency to NUMA-converge
            1.783 secs slowest (max) thread-runtime
            1.000 secs fastest (min) thread-runtime
            1.633 secs average thread-runtime
           21.960 % difference between max/avg runtime
            1.345 GB data processed, per thread
           21.517 GB data processed, total
            1.326 nsecs/byte/thread runtime
            0.754 GB/sec/thread speed
           12.067 GB/sec total speed

   # Running  4x6-convergence, "perf bench numa mem -p 4 -t 6 -P 1020 -s 100 -zZ0qcm --thp  1"
            5.396 secs latency to NUMA-converge
            5.396 secs slowest (max) thread-runtime
            4.000 secs fastest (min) thread-runtime
            4.928 secs average thread-runtime
           12.937 % difference between max/avg runtime
            2.721 GB data processed, per thread
           65.306 GB data processed, total
            1.983 nsecs/byte/thread runtime
            0.504 GB/sec/thread speed
           12.102 GB/sec total speed

   # Running  4x8-convergence, "perf bench numa mem -p 4 -t 8 -P 512 -s 100 -zZ0qcm --thp  1"
            3.121 secs latency to NUMA-converge
            3.121 secs slowest (max) thread-runtime
            2.000 secs fastest (min) thread-runtime
            2.836 secs average thread-runtime
           17.962 % difference between max/avg runtime
            1.194 GB data processed, per thread
           38.192 GB data processed, total
            2.615 nsecs/byte/thread runtime
            0.382 GB/sec/thread speed
           12.236 GB/sec total speed

   # Running  8x4-convergence, "perf bench numa mem -p 8 -t 4 -P 512 -s 100 -zZ0qcm --thp  1"
            4.302 secs latency to NUMA-converge
            4.302 secs slowest (max) thread-runtime
            3.000 secs fastest (min) thread-runtime
            4.045 secs average thread-runtime
           15.133 % difference between max/avg runtime
            1.631 GB data processed, per thread
           52.178 GB data processed, total
            2.638 nsecs/byte/thread runtime
            0.379 GB/sec/thread speed
           12.128 GB/sec total speed

   # Running  8x4-convergence-NOTHP, "perf bench numa mem -p 8 -t 4 -P 512 -s 100 -zZ0qcm --thp  1 --thp -1"
            4.418 secs latency to NUMA-converge
            4.418 secs slowest (max) thread-runtime
            3.000 secs fastest (min) thread-runtime
            4.104 secs average thread-runtime
           16.045 % difference between max/avg runtime
            1.664 GB data processed, per thread
           53.254 GB data processed, total
            2.655 nsecs/byte/thread runtime
            0.377 GB/sec/thread speed
           12.055 GB/sec total speed

   # Running  3x1-convergence, "perf bench numa mem -p 3 -t 1 -P 512 -s 100 -zZ0qcm --thp  1"
            0.973 secs latency to NUMA-converge
            0.973 secs slowest (max) thread-runtime
            0.000 secs fastest (min) thread-runtime
            0.955 secs average thread-runtime
           50.000 % difference between max/avg runtime
            4.124 GB data processed, per thread
           12.372 GB data processed, total
            0.236 nsecs/byte/thread runtime
            4.238 GB/sec/thread speed
           12.715 GB/sec total speed

   # Running  4x1-convergence, "perf bench numa mem -p 4 -t 1 -P 512 -s 100 -zZ0qcm --thp  1"
            0.820 secs latency to NUMA-converge
            0.820 secs slowest (max) thread-runtime
            0.000 secs fastest (min) thread-runtime
            0.808 secs average thread-runtime
           50.000 % difference between max/avg runtime
            2.555 GB data processed, per thread
           10.220 GB data processed, total
            0.321 nsecs/byte/thread runtime
            3.117 GB/sec/thread speed
           12.468 GB/sec total speed

   # Running  8x1-convergence, "perf bench numa mem -p 8 -t 1 -P 512 -s 100 -zZ0qcm --thp  1"
            0.667 secs latency to NUMA-converge
            0.667 secs slowest (max) thread-runtime
            0.000 secs fastest (min) thread-runtime
            0.607 secs average thread-runtime
           50.000 % difference between max/avg runtime
            1.009 GB data processed, per thread
            8.069 GB data processed, total
            0.661 nsecs/byte/thread runtime
            1.512 GB/sec/thread speed
           12.095 GB/sec total speed

   # Running 16x1-convergence, "perf bench numa mem -p 16 -t 1 -P 256 -s 100 -zZ0qcm --thp  1"
            1.546 secs latency to NUMA-converge
            1.546 secs slowest (max) thread-runtime
            1.000 secs fastest (min) thread-runtime
            1.485 secs average thread-runtime
           17.664 % difference between max/avg runtime
            1.162 GB data processed, per thread
           18.594 GB data processed, total
            1.331 nsecs/byte/thread runtime
            0.752 GB/sec/thread speed
           12.025 GB/sec total speed

   # Running 32x1-convergence, "perf bench numa mem -p 32 -t 1 -P 128 -s 100 -zZ0qcm --thp  1"
            0.812 secs latency to NUMA-converge
            0.812 secs slowest (max) thread-runtime
            0.000 secs fastest (min) thread-runtime
            0.739 secs average thread-runtime
           50.000 % difference between max/avg runtime
            0.309 GB data processed, per thread
            9.874 GB data processed, total
            2.630 nsecs/byte/thread runtime
            0.380 GB/sec/thread speed
           12.166 GB/sec total speed

   # Running  2x1-bw-process, "perf bench numa mem -p 2 -t 1 -P 1024 -s 20 -zZ0q --thp  1"
           20.044 secs slowest (max) thread-runtime
           20.000 secs fastest (min) thread-runtime
           20.020 secs average thread-runtime
            0.109 % difference between max/avg runtime
          125.750 GB data processed, per thread
          251.501 GB data processed, total
            0.159 nsecs/byte/thread runtime
            6.274 GB/sec/thread speed
           12.548 GB/sec total speed

   # Running  3x1-bw-process, "perf bench numa mem -p 3 -t 1 -P 1024 -s 20 -zZ0q --thp  1"
           20.148 secs slowest (max) thread-runtime
           20.000 secs fastest (min) thread-runtime
           20.090 secs average thread-runtime
            0.367 % difference between max/avg runtime
           85.267 GB data processed, per thread
          255.800 GB data processed, total
            0.236 nsecs/byte/thread runtime
            4.232 GB/sec/thread speed
           12.696 GB/sec total speed

   # Running  4x1-bw-process, "perf bench numa mem -p 4 -t 1 -P 1024 -s 20 -zZ0q --thp  1"
           20.169 secs slowest (max) thread-runtime
           20.000 secs fastest (min) thread-runtime
           20.100 secs average thread-runtime
            0.419 % difference between max/avg runtime
           63.144 GB data processed, per thread
          252.576 GB data processed, total
            0.319 nsecs/byte/thread runtime
            3.131 GB/sec/thread speed
           12.523 GB/sec total speed

   # Running  8x1-bw-process, "perf bench numa mem -p 8 -t 1 -P  512 -s 20 -zZ0q --thp  1"
           20.175 secs slowest (max) thread-runtime
           20.000 secs fastest (min) thread-runtime
           20.107 secs average thread-runtime
            0.433 % difference between max/avg runtime
           31.267 GB data processed, per thread
          250.133 GB data processed, total
            0.645 nsecs/byte/thread runtime
            1.550 GB/sec/thread speed
           12.398 GB/sec total speed

   # Running  8x1-bw-process-NOTHP, "perf bench numa mem -p 8 -t 1 -P  512 -s 20 -zZ0q --thp  1 --thp -1"
           20.216 secs slowest (max) thread-runtime
           20.000 secs fastest (min) thread-runtime
           20.113 secs average thread-runtime
            0.535 % difference between max/avg runtime
           30.998 GB data processed, per thread
          247.981 GB data processed, total
            0.652 nsecs/byte/thread runtime
            1.533 GB/sec/thread speed
           12.266 GB/sec total speed

   # Running 16x1-bw-process, "perf bench numa mem -p 16 -t 1 -P 256 -s 20 -zZ0q --thp  1"
           20.234 secs slowest (max) thread-runtime
           20.000 secs fastest (min) thread-runtime
           20.174 secs average thread-runtime
            0.577 % difference between max/avg runtime
           15.377 GB data processed, per thread
          246.039 GB data processed, total
            1.316 nsecs/byte/thread runtime
            0.760 GB/sec/thread speed
           12.160 GB/sec total speed

   # Running  1x4-bw-thread, "perf bench numa mem -p 1 -t 4 -T 256 -s 20 -zZ0q --thp  1"
           20.040 secs slowest (max) thread-runtime
           20.000 secs fastest (min) thread-runtime
           20.028 secs average thread-runtime
            0.099 % difference between max/avg runtime
           66.832 GB data processed, per thread
          267.328 GB data processed, total
            0.300 nsecs/byte/thread runtime
            3.335 GB/sec/thread speed
           13.340 GB/sec total speed

   # Running  1x8-bw-thread, "perf bench numa mem -p 1 -t 8 -T 256 -s 20 -zZ0q --thp  1"
           20.064 secs slowest (max) thread-runtime
           20.000 secs fastest (min) thread-runtime
           20.034 secs average thread-runtime
            0.160 % difference between max/avg runtime
           32.911 GB data processed, per thread
          263.286 GB data processed, total
            0.610 nsecs/byte/thread runtime
            1.640 GB/sec/thread speed
           13.122 GB/sec total speed

   # Running 1x16-bw-thread, "perf bench numa mem -p 1 -t 16 -T 128 -s 20 -zZ0q --thp  1"
           20.092 secs slowest (max) thread-runtime
           20.000 secs fastest (min) thread-runtime
           20.052 secs average thread-runtime
            0.230 % difference between max/avg runtime
           16.131 GB data processed, per thread
          258.088 GB data processed, total
            1.246 nsecs/byte/thread runtime
            0.803 GB/sec/thread speed
           12.845 GB/sec total speed

   # Running 1x32-bw-thread, "perf bench numa mem -p 1 -t 32 -T 64 -s 20 -zZ0q --thp  1"
           20.099 secs slowest (max) thread-runtime
           20.000 secs fastest (min) thread-runtime
           20.063 secs average thread-runtime
            0.247 % difference between max/avg runtime
            7.962 GB data processed, per thread
          254.773 GB data processed, total
            2.525 nsecs/byte/thread runtime
            0.396 GB/sec/thread speed
           12.676 GB/sec total speed

   # Running  2x3-bw-process, "perf bench numa mem -p 2 -t 3 -P 512 -s 20 -zZ0q --thp  1"
           20.150 secs slowest (max) thread-runtime
           20.000 secs fastest (min) thread-runtime
           20.120 secs average thread-runtime
            0.372 % difference between max/avg runtime
           44.827 GB data processed, per thread
          268.960 GB data processed, total
            0.450 nsecs/byte/thread runtime
            2.225 GB/sec/thread speed
           13.348 GB/sec total speed

   # Running  4x4-bw-process, "perf bench numa mem -p 4 -t 4 -P 512 -s 20 -zZ0q --thp  1"
           20.258 secs slowest (max) thread-runtime
           20.000 secs fastest (min) thread-runtime
           20.168 secs average thread-runtime
            0.636 % difference between max/avg runtime
           17.079 GB data processed, per thread
          273.263 GB data processed, total
            1.186 nsecs/byte/thread runtime
            0.843 GB/sec/thread speed
           13.489 GB/sec total speed

   # Running  4x6-bw-process, "perf bench numa mem -p 4 -t 6 -P 512 -s 20 -zZ0q --thp  1"
           20.559 secs slowest (max) thread-runtime
           20.000 secs fastest (min) thread-runtime
           20.382 secs average thread-runtime
            1.359 % difference between max/avg runtime
           10.758 GB data processed, per thread
          258.201 GB data processed, total
            1.911 nsecs/byte/thread runtime
            0.523 GB/sec/thread speed
           12.559 GB/sec total speed

   # Running  4x8-bw-process, "perf bench numa mem -p 4 -t 8 -P 512 -s 20 -zZ0q --thp  1"
           20.744 secs slowest (max) thread-runtime
           20.000 secs fastest (min) thread-runtime
           20.516 secs average thread-runtime
            1.792 % difference between max/avg runtime
            8.069 GB data processed, per thread
          258.201 GB data processed, total
            2.571 nsecs/byte/thread runtime
            0.389 GB/sec/thread speed
           12.447 GB/sec total speed

   # Running  4x8-bw-process-NOTHP, "perf bench numa mem -p 4 -t 8 -P 512 -s 20 -zZ0q --thp  1 --thp -1"
           20.855 secs slowest (max) thread-runtime
           20.000 secs fastest (min) thread-runtime
           20.561 secs average thread-runtime
            2.050 % difference between max/avg runtime
            8.069 GB data processed, per thread
          258.201 GB data processed, total
            2.585 nsecs/byte/thread runtime
            0.387 GB/sec/thread speed
           12.381 GB/sec total speed

   # Running  3x3-bw-process, "perf bench numa mem -p 3 -t 3 -P 512 -s 20 -zZ0q --thp  1"
           20.134 secs slowest (max) thread-runtime
           20.000 secs fastest (min) thread-runtime
           20.077 secs average thread-runtime
            0.333 % difference between max/avg runtime
           28.091 GB data processed, per thread
          252.822 GB data processed, total
            0.717 nsecs/byte/thread runtime
            1.395 GB/sec/thread speed
           12.557 GB/sec total speed

   # Running  5x5-bw-process, "perf bench numa mem -p 5 -t 5 -P 512 -s 20 -zZ0q --thp  1"
           20.588 secs slowest (max) thread-runtime
           20.000 secs fastest (min) thread-runtime
           20.375 secs average thread-runtime
            1.427 % difference between max/avg runtime
           10.177 GB data processed, per thread
          254.436 GB data processed, total
            2.023 nsecs/byte/thread runtime
            0.494 GB/sec/thread speed
           12.359 GB/sec total speed

   # Running 2x16-bw-process, "perf bench numa mem -p 2 -t 16 -P 512 -s 20 -zZ0q --thp  1"
           20.657 secs slowest (max) thread-runtime
           20.000 secs fastest (min) thread-runtime
           20.429 secs average thread-runtime
            1.589 % difference between max/avg runtime
            8.170 GB data processed, per thread
          261.429 GB data processed, total
            2.528 nsecs/byte/thread runtime
            0.395 GB/sec/thread speed
           12.656 GB/sec total speed

   # Running 1x32-bw-process, "perf bench numa mem -p 1 -t 32 -P 2048 -s 20 -zZ0q --thp  1"
           22.981 secs slowest (max) thread-runtime
           20.000 secs fastest (min) thread-runtime
           21.996 secs average thread-runtime
            6.486 % difference between max/avg runtime
            8.863 GB data processed, per thread
          283.606 GB data processed, total
            2.593 nsecs/byte/thread runtime
            0.386 GB/sec/thread speed
           12.341 GB/sec total speed

   # Running numa02-bw, "perf bench numa mem -p 1 -t 32 -T 32 -s 20 -zZ0q --thp  1"
           20.047 secs slowest (max) thread-runtime
           19.000 secs fastest (min) thread-runtime
           20.026 secs average thread-runtime
            2.611 % difference between max/avg runtime
            8.441 GB data processed, per thread
          270.111 GB data processed, total
            2.375 nsecs/byte/thread runtime
            0.421 GB/sec/thread speed
           13.474 GB/sec total speed

   # Running numa02-bw-NOTHP, "perf bench numa mem -p 1 -t 32 -T 32 -s 20 -zZ0q --thp  1 --thp -1"
           20.088 secs slowest (max) thread-runtime
           19.000 secs fastest (min) thread-runtime
           20.025 secs average thread-runtime
            2.709 % difference between max/avg runtime
            8.411 GB data processed, per thread
          269.142 GB data processed, total
            2.388 nsecs/byte/thread runtime
            0.419 GB/sec/thread speed
           13.398 GB/sec total speed

   # Running numa01-bw-thread, "perf bench numa mem -p 2 -t 16 -T 192 -s 20 -zZ0q --thp  1"
           20.293 secs slowest (max) thread-runtime
           20.000 secs fastest (min) thread-runtime
           20.175 secs average thread-runtime
            0.721 % difference between max/avg runtime
            7.918 GB data processed, per thread
          253.374 GB data processed, total
            2.563 nsecs/byte/thread runtime
            0.390 GB/sec/thread speed
           12.486 GB/sec total speed

   # Running numa01-bw-thread-NOTHP, "perf bench numa mem -p 2 -t 16 -T 192 -s 20 -zZ0q --thp  1 --thp -1"
           20.411 secs slowest (max) thread-runtime
           20.000 secs fastest (min) thread-runtime
           20.226 secs average thread-runtime
            1.006 % difference between max/avg runtime
            7.931 GB data processed, per thread
          253.778 GB data processed, total
            2.574 nsecs/byte/thread runtime
            0.389 GB/sec/thread speed
           12.434 GB/sec total speed

  #

Signed-off-by: Ian Rogers <irogers@google.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Link: https://lore.kernel.org/r/20201012161611.366482-1-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 46 insertions, 21 deletions

diff --git a/tools/perf/bench/numa.c b/tools/perf/bench/numa.c
index f85bceccc459..11726ec6285f 100644
--- a/tools/perf/bench/numa.c
+++ b/tools/perf/bench/numa.c
@@ -137,12 +137,13 @@ struct global_info {
 	u8			*data;
 
 	pthread_mutex_t		startup_mutex;
+	pthread_cond_t		startup_cond;
 	int			nr_tasks_started;
 
-	pthread_mutex_t		startup_done_mutex;
-
 	pthread_mutex_t		start_work_mutex;
+	pthread_cond_t		start_work_cond;
 	int			nr_tasks_working;
+	bool			start_work;
 
 	pthread_mutex_t		stop_work_mutex;
 	u64			bytes_done;
@@ -483,6 +484,18 @@ static void init_global_mutex(pthread_mutex_t *mutex)
 	pthread_mutex_init(mutex, &attr);
 }
 
+/*
+ * Return a process-shared (global) condition variable:
+ */
+static void init_global_cond(pthread_cond_t *cond)
+{
+	pthread_condattr_t attr;
+
+	pthread_condattr_init(&attr);
+	pthread_condattr_setpshared(&attr, PTHREAD_PROCESS_SHARED);
+	pthread_cond_init(cond, &attr);
+}
+
 static int parse_cpu_list(const char *arg)
 {
 	p0.cpu_list_str = strdup(arg);
@@ -1136,15 +1149,18 @@ static void *worker_thread(void *__tdata)
 	if (g->p.serialize_startup) {
 		pthread_mutex_lock(&g->startup_mutex);
 		g->nr_tasks_started++;
+		/* The last thread wakes the main process. */
+		if (g->nr_tasks_started == g->p.nr_tasks)
+			pthread_cond_signal(&g->startup_cond);
+
 		pthread_mutex_unlock(&g->startup_mutex);
 
 		/* Here we will wait for the main process to start us all at once: */
 		pthread_mutex_lock(&g->start_work_mutex);
+		g->start_work = false;
 		g->nr_tasks_working++;
-
-		/* Last one wake the main process: */
-		if (g->nr_tasks_working == g->p.nr_tasks)
-			pthread_mutex_unlock(&g->startup_done_mutex);
+		while (!g->start_work)
+			pthread_cond_wait(&g->start_work_cond, &g->start_work_mutex);
 
 		pthread_mutex_unlock(&g->start_work_mutex);
 	}
@@ -1441,8 +1457,9 @@ static int init(void)
 
 	/* Startup serialization: */
 	init_global_mutex(&g->start_work_mutex);
+	init_global_cond(&g->start_work_cond);
 	init_global_mutex(&g->startup_mutex);
-	init_global_mutex(&g->startup_done_mutex);
+	init_global_cond(&g->startup_cond);
 	init_global_mutex(&g->stop_work_mutex);
 
 	init_thread_data();
@@ -1502,9 +1519,6 @@ static int __bench_numa(const char *name)
 	pids = zalloc(g->p.nr_proc * sizeof(*pids));
 	pid = -1;
 
-	/* All threads try to acquire it, this way we can wait for them to start up: */
-	pthread_mutex_lock(&g->start_work_mutex);
-
 	if (g->p.serialize_startup) {
 		tprintf(" #\n");
 		tprintf(" # Startup synchronization: ..."); fflush(stdout);
@@ -1526,22 +1540,29 @@ static int __bench_numa(const char *name)
 		pids[i] = pid;
 
 	}
-	/* Wait for all the threads to start up: */
-	while (g->nr_tasks_started != g->p.nr_tasks)
-		usleep(USEC_PER_MSEC);
-
-	BUG_ON(g->nr_tasks_started != g->p.nr_tasks);
 
 	if (g->p.serialize_startup) {
+		bool threads_ready = false;
 		double startup_sec;
 
-		pthread_mutex_lock(&g->startup_done_mutex);
+		/*
+		 * Wait for all the threads to start up. The last thread will
+		 * signal this process.
+		 */
+		pthread_mutex_lock(&g->startup_mutex);
+		while (g->nr_tasks_started != g->p.nr_tasks)
+			pthread_cond_wait(&g->startup_cond, &g->startup_mutex);
 
-		/* This will start all threads: */
-		pthread_mutex_unlock(&g->start_work_mutex);
+		pthread_mutex_unlock(&g->startup_mutex);
 
-		/* This mutex is locked - the last started thread will wake us: */
-		pthread_mutex_lock(&g->startup_done_mutex);
+		/* Wait for all threads to be at the start_work_cond. */
+		while (!threads_ready) {
+			pthread_mutex_lock(&g->start_work_mutex);
+			threads_ready = (g->nr_tasks_working == g->p.nr_tasks);
+			pthread_mutex_unlock(&g->start_work_mutex);
+			if (!threads_ready)
+				usleep(1);
+		}
 
 		gettimeofday(&stop, NULL);
 
@@ -1555,7 +1576,11 @@ static int __bench_numa(const char *name)
 		tprintf(" #\n");
 
 		start = stop;
-		pthread_mutex_unlock(&g->startup_done_mutex);
+		/* Start all threads running. */
+		pthread_mutex_lock(&g->start_work_mutex);
+		g->start_work = true;
+		pthread_mutex_unlock(&g->start_work_mutex);
+		pthread_cond_broadcast(&g->start_work_cond);
 	} else {
 		gettimeofday(&start, NULL);
 	}