diff --git a/benchtests/Makefile b/benchtests/Makefile
index 08603a2..343e56f 100644
--- a/benchtests/Makefile
+++ b/benchtests/Makefile
@@ -44,9 +44,10 @@ benchset := $(string-bench-all) $(stdlib-bench)
  CFLAGS-bench-ffs.c += -fno-builtin
  CFLAGS-bench-ffsll.c += -fno-builtin

-bench-malloc := malloc-thread
+bench-malloc := malloc-thread malloc-concurrent

  $(addprefix $(objpfx)bench-,$(bench-math)): $(libm)
  $(addprefix $(objpfx)bench-,$(bench-pthread)): $(shared-thread-library)
  $(objpfx)bench-malloc-thread: $(shared-thread-library)
+$(objpfx)bench-malloc-concurrent: $(shared-thread-library)

@@ -116,10 +117,11 @@ bench-set: $(binaries-benchset)
  	done

  bench-malloc: $(binaries-bench-malloc)
-	run=$(objpfx)bench-malloc-thread; \
-	for thr in 1 8 16 32; do \
-	  echo "Running $${run} $${thr}"; \
-	  $(run-bench) $${thr} > $${run}-$${thr}.out; \
+	for run in $^; do \
+	  for thr in 1 8 16 32; do \
+	    echo "Running $${run} $${thr}"; \
+	    $(run-bench) $${thr} > $${run}-$${thr}.out; \
+	  done; \
  	done

  # Build and execute the benchmark functions.  This target generates JSON

diff --git a/benchtests/bench-malloc-concurrent.c 
b/benchtests/bench-malloc-concurrent.c
index e69de29..75bd586 100644
--- a/benchtests/bench-malloc-concurrent.c
+++ b/benchtests/bench-malloc-concurrent.c
@@ -0,0 +1,315 @@
+/* Benchmark malloc and free functions.
+   Copyright (C) 2013-2015 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <math.h>
+#include <pthread.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/time.h>
+#include <sys/resource.h>
+#include <unistd.h>
+
+#include "bench-timing.h"
+#include "json-lib.h"
+
+/* Benchmark duration in seconds.  */
+#define BENCHMARK_DURATION	60
+#define RAND_SEED		88
+
+#ifndef NUM_THREADS
+# define NUM_THREADS 1
+#endif
+
+/* Maximum memory that can be allocated at any one time is:
+
+   NUM_THREADS * WORKING_SET_SIZE * MAX_ALLOCATION_SIZE
+
+   However due to the distribution of the random block sizes
+   the typical amount allocated will be much smaller.  */
+#define WORKING_SET_SIZE	1024
+
+#define MIN_ALLOCATION_SIZE	4
+#define MAX_ALLOCATION_SIZE	32768
+
+/* Get a random block size with an inverse square distribution.  */
+static unsigned int
+get_block_size (unsigned int rand_data)
+{
+  /* Inverse square.  */
+  const float exponent = -2;
+  /* Minimum value of distribution.  */
+  const float dist_min = MIN_ALLOCATION_SIZE;
+  /* Maximum value of distribution.  */
+  const float dist_max = MAX_ALLOCATION_SIZE;
+
+  float min_pow = powf (dist_min, exponent + 1);
+  float max_pow = powf (dist_max, exponent + 1);
+
+  float r = (float) rand_data / RAND_MAX;
+
+  return (unsigned int) powf ((max_pow - min_pow) * r + min_pow,
+			      1 / (exponent + 1));
+}
+
+static pthread_mutex_t index_lock[WORKING_SET_SIZE];
+
+static void
+init_index_locks (void)
+{
+  for (size_t i = 0; i < WORKING_SET_SIZE; i++)
+    pthread_mutex_init (&index_lock[i], 0);
+}
+
+#define NUM_BLOCK_SIZES	8000
+#define NUM_OFFSETS	((WORKING_SET_SIZE) * 4)
+
+static unsigned int random_block_sizes[NUM_BLOCK_SIZES];
+static unsigned int random_offsets[NUM_OFFSETS];
+
+static void
+init_random_values (void)
+{
+  for (size_t i = 0; i < NUM_BLOCK_SIZES; i++)
+    random_block_sizes[i] = get_block_size (rand ());
+
+  for (size_t i = 0; i < NUM_OFFSETS; i++)
+    random_offsets[i] = rand () % WORKING_SET_SIZE;
+}
+
+static unsigned int
+get_random_block_size (unsigned int *state)
+{
+  unsigned int idx = *state;
+
+  if (idx >= NUM_BLOCK_SIZES - 1)
+    idx = 0;
+  else
+    idx++;
+
+  *state = idx;
+
+  return random_block_sizes[idx];
+}
+
+static unsigned int
+get_random_offset (unsigned int *state)
+{
+  unsigned int idx = *state;
+
+  if (idx >= NUM_OFFSETS - 1)
+    idx = 0;
+  else
+    idx++;
+
+  *state = idx;
+
+  return random_offsets[idx];
+}
+
+static volatile bool timeout;
+
+static void
+alarm_handler (int signum)
+{
+  timeout = true;
+}
+
+/* Allocate and free blocks in a random order.  */
+static size_t
+malloc_benchmark_loop (void **ptr_arr, size_t start_offset)
+{
+  unsigned int offset_state = start_offset, block_state = 0;
+  size_t iters = 0;
+
+  while (!timeout)
+    {
+      unsigned int next_idx = get_random_offset (&offset_state);
+      unsigned int next_block = get_random_block_size (&block_state);
+
+      pthread_mutex_lock (&index_lock[next_idx]);
+      free (ptr_arr[next_idx]);
+      ptr_arr[next_idx] = malloc (next_block);
+      pthread_mutex_unlock (&index_lock[next_idx]);
+
+      iters++;
+    }
+
+  return iters;
+}
+
+struct thread_args
+{
+  size_t iters;
+  size_t start_offset;
+  void **working_set;
+  timing_t elapsed;
+};
+
+static void *
+benchmark_thread (void *arg)
+{
+  struct thread_args *args = (struct thread_args *) arg;
+  size_t iters;
+  void *thread_set = args->working_set;
+  timing_t start, stop;
+
+  TIMING_NOW (start);
+  iters = malloc_benchmark_loop (thread_set, args->start_offset);
+  TIMING_NOW (stop);
+
+  TIMING_DIFF (args->elapsed, start, stop);
+  args->iters = iters;
+
+  return NULL;
+}
+
+static timing_t
+do_benchmark (size_t num_threads, size_t *iters)
+{
+  timing_t elapsed = 0;
+
+  if (num_threads == 1)
+    {
+      timing_t start, stop;
+      void *working_set[WORKING_SET_SIZE];
+
+      memset (working_set, 0, sizeof (working_set));
+
+      TIMING_NOW (start);
+      *iters = malloc_benchmark_loop (working_set, 0);
+      TIMING_NOW (stop);
+
+      TIMING_DIFF (elapsed, start, stop);
+    }
+  else
+    {
+      struct thread_args args[num_threads];
+      void *working_set[WORKING_SET_SIZE];
+      pthread_t threads[num_threads];
+
+      memset (working_set, 0, sizeof (working_set));
+
+      *iters = 0;
+
+      for (size_t i = 0; i < num_threads; i++)
+	{
+	  args[i].working_set = working_set;
+	  args[i].start_offset = (WORKING_SET_SIZE / num_threads) * i;
+	  pthread_create(&threads[i], NULL, benchmark_thread, &args[i]);
+	}
+
+      for (size_t i = 0; i < num_threads; i++)
+	{
+	  pthread_join(threads[i], NULL);
+	  TIMING_ACCUM (elapsed, args[i].elapsed);
+	  *iters += args[i].iters;
+	}
+    }
+  return elapsed;
+}
+
+static void usage(const char *name)
+{
+  fprintf (stderr, "%s: <num_threads>\n", name);
+  exit (1);
+}
+
+int
+main (int argc, char **argv)
+{
+  timing_t cur;
+  size_t iters = 0, num_threads = 1;
+  unsigned long res;
+  json_ctx_t json_ctx;
+  double d_total_s, d_total_i;
+  struct sigaction act;
+
+  if (argc == 1)
+    num_threads = 1;
+  else if (argc == 2)
+    {
+      long ret;
+
+      errno = 0;
+      ret = strtol(argv[1], NULL, 10);
+
+      if (errno || ret == 0)
+	usage(argv[0]);
+
+      num_threads = ret;
+    }
+  else
+    usage(argv[0]);
+
+  init_index_locks ();
+  init_random_values ();
+
+  json_init (&json_ctx, 0, stdout);
+
+  json_document_begin (&json_ctx);
+
+  json_attr_string (&json_ctx, "timing_type", TIMING_TYPE);
+
+  json_attr_object_begin (&json_ctx, "functions");
+
+  json_attr_object_begin (&json_ctx, "malloc");
+
+  json_attr_object_begin (&json_ctx, "");
+
+  TIMING_INIT (res);
+
+  (void) res;
+
+  memset (&act, 0, sizeof (act));
+  act.sa_handler = &alarm_handler;
+
+  sigaction (SIGALRM, &act, NULL);
+
+  alarm (BENCHMARK_DURATION);
+
+  cur = do_benchmark (num_threads, &iters);
+
+  struct rusage usage;
+  getrusage(RUSAGE_SELF, &usage);
+
+  d_total_s = cur;
+  d_total_i = iters;
+
+  json_attr_double (&json_ctx, "duration", d_total_s);
+  json_attr_double (&json_ctx, "iterations", d_total_i);
+  json_attr_double (&json_ctx, "time_per_iteration", d_total_s / d_total_i);
+  json_attr_double (&json_ctx, "max_rss", usage.ru_maxrss);
+
+  json_attr_double (&json_ctx, "threads", num_threads);
+  json_attr_double (&json_ctx, "min_size", MIN_ALLOCATION_SIZE);
+  json_attr_double (&json_ctx, "max_size", MAX_ALLOCATION_SIZE);
+  json_attr_double (&json_ctx, "random_seed", RAND_SEED);
+
+  json_attr_object_end (&json_ctx);
+
+  json_attr_object_end (&json_ctx);
+
+  json_attr_object_end (&json_ctx);
+
+  json_document_end (&json_ctx);
+
+  return 0;
+}
