5 files changed, 160 insertions, 0 deletions
diff --git a/src/tools/README.md b/src/tools/README.md
index 7b9b184..89b6c39 100644
--- a/src/tools/README.md
+++ b/src/tools/README.md
@@ -18,3 +18,4 @@
 - [column](./column.md)
 - [sort](./sort.md)
 - [sed](./sed.md)
+- [gnuplot](./gnuplot.md)
diff --git a/src/tools/gnuplot.md b/src/tools/gnuplot.md
new file mode 100644
index 0000000..0a2f50f
--- /dev/null
+++ b/src/tools/gnuplot.md
@@ -0,0 +1,68 @@
+# gnuplot (1)
+
+```
+# Launch interactive shell.
+gnuplot
+
+# Launch interactive shell.
+gnuplot [opt]
+  opt:
+    -p ................ persist plot window
+    -c <file> ......... run script file
+    -e "<cmd1>; .." ... run cmd(s)
+```
+
+## Frequently used configuration
+```sh
+# Plot title.
+set title "the plot"
+
+# Labels.
+set xlabel "abc"
+set ylabel "def"
+
+# Output format, 'help set term' for all output formats.
+set term svg
+# Output file.
+set output "out.svg"
+
+# Make axis logarithmic to given base.
+set logscale x 2
+
+# Change separator, default is whitespace.
+set datafile separator ","
+```
+
+## Plot
+```sh
+# With specific style (eg lines, linespoint, boxes, steps, impulses, ..).
+plot "<data_file>" with <plot_style>
+
+> cat data.txt
+1 1 3
+2 2 2
+3 3 1
+4 2 2
+
+# Plot specific column.
+plot "data.txt" using 1:2, "data.txt" using 1:3
+# Equivalent using the special file "", which re-uses the previous input file.
+plot "data.txt" using 1:2, "" using 1:3
+
+# Plot piped data.
+plot "< head -n2 data.txt"
+
+# Plot with alternate title.
+plot "data.txt" title "moose"
+```
+
+## Example: multiple data sets in on plot
+```sh
+{{#include gnuplot/mem_lat.plot}}
+```
+
+On Linux x86_64, [`mem_lat.c`](gnuplot/mem_lat.c) provides an example which can
+be run as follows.
+```sh
+{{#include gnuplot/plot.sh:3:9}}
+```
diff --git a/src/tools/gnuplot/mem_lat.c b/src/tools/gnuplot/mem_lat.c
new file mode 100644
index 0000000..b85a08f
--- /dev/null
+++ b/src/tools/gnuplot/mem_lat.c
@@ -0,0 +1,67 @@
+#include <assert.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+enum : size_t {
+  KB = 1024,
+  MB = 1024 * KB,
+
+  DFL_MAXSZ  = 64 * MB,
+  DFL_STRIDE = 256,
+  NUM_ACCESS = 1ull << 24,
+};
+
+static inline uint64_t rdtsc() {
+  uint32_t eax, edx;
+  asm volatile("rdtsc" : "=a"(eax), "=d"(edx));
+  return ((uint64_t)edx << 32) | eax;
+}
+
+uint64_t run_one_walk(size_t size, size_t stride) {
+  // Check size is power of two.
+  assert((size & (size -1)) == 0);
+  assert((size / stride) <= NUM_ACCESS);
+
+  unsigned char *mem = (unsigned char *)malloc(size);
+  memset(mem, 0x55, size);
+
+  const uint64_t start = rdtsc();
+  for (size_t it = 0; it < NUM_ACCESS; it++) {
+    ((volatile unsigned char *)mem)[(it * stride) & (size - 1)]++;
+  }
+  const uint64_t stop = rdtsc();
+
+  free(mem);
+  return stop - start;
+}
+
+int main(int argc, char *argv[]) {
+  size_t max_sz = DFL_MAXSZ;
+  size_t stride = DFL_STRIDE;
+
+  if (argc > 1) {
+    max_sz = strtoll(argv[1], 0, 10);
+    max_sz *= MB;
+  }
+  if (argc > 2) {
+    stride = strtoll(argv[2], 0, 10);
+  }
+
+  fprintf(stderr, "max_sz=%zuK stride=%zu access=%zu\n",
+          max_sz / KB, stride, NUM_ACCESS);
+
+  size_t size = 2048;
+  while (size <= max_sz) {
+    uint64_t cycles = 0;
+    for (size_t loop = 0; loop < 10; ++loop) {
+      cycles += run_one_walk(size, stride);
+    }
+    printf("%6zuK %f\n", size / KB, (double)cycles / NUM_ACCESS / 10.0);
+
+    size *= 2;
+  }
+
+  return 0;
+}
diff --git a/src/tools/gnuplot/mem_lat.plot b/src/tools/gnuplot/mem_lat.plot
new file mode 100644
index 0000000..db058f9
--- /dev/null
+++ b/src/tools/gnuplot/mem_lat.plot
@@ -0,0 +1,13 @@
+# file: mem_lat.plot
+
+set title  "memory latency (different strides)"
+set xlabel "array in KB"
+set ylabel "cycles / access"
+
+set logscale x 2
+
+plot "stride_32.txt"  title "32"  with linespoints, \
+     "stride_64.txt"  title "64"  with linespoints, \
+     "stride_128.txt" title "128" with linespoints, \
+     "stride_256.txt" title "256" with linespoints, \
+     "stride_512.txt" title "512" with linespoints
diff --git a/src/tools/gnuplot/plot.sh b/src/tools/gnuplot/plot.sh
new file mode 100644
index 0000000..e288c6c
--- /dev/null
+++ b/src/tools/gnuplot/plot.sh
@@ -0,0 +1,11 @@
+#!/bin/bash
+
+gcc -o mem_lat mem_lat.c -g -O3 -Wall -Werror
+
+for stride in 32 64 128 256 512; do \
+    taskset -c 1 ./mem_lat 128 $stride | tee stride_$stride.txt ; \
+done
+
+gnuplot -p -c mem_lat.plot
+
+rm -f stride_*.txt mem_lat