ok, add a bench source

This new source acts like other sources (GMs, SKPs) for benchmarks.  It
times multiple samples (controlled by samples=N, default 20), and each
of those samples uses the same strategy as monobench, growing loops
exponentially until it runs for at least 10ms.

When done it prints the fastest and the two slowest samples.  In
practice the 100th percentile sample is very different from the
next slowest due to caching, and the fastest is always interesting.

Because these benchmarks run in whatever execution engine ok has
selected, on non-Windows platforms you have some real control over the
interaction between benchmarks.  In its default "fork" mode each
benchmark runs independently in its own process, so the 100th
percentiles really stand out.  The other modes "thread" and "serial"
work as you'd expect too.

Here's an example where you can see how the different interactions work:

out/ok bench:samples=100 8888 filter:search=text_16_AA fork
    [text_16_AA_WT] 2.32µs  @0  6.23µs  @99 24.3ms  @100
    [text_16_AA_FF] 2.41µs  @0  5.7µs   @99 23.3ms  @100
    [text_16_AA_88] 2.55µs  @0  5.6µs   @99 24.8ms  @100
    [text_16_AA_BK] 1.97µs  @0  5.44µs  @99 23.2ms  @100

out/ok bench:samples=100 8888 filter:search=text_16_AA thread
    [text_16_AA_FF] 2.45µs  @0  23.5µs  @99 24.8ms  @100
    [text_16_AA_WT] 2.52µs  @0  17.8µs  @99 24.7ms  @100
    [text_16_AA_88] 2.55µs  @0  19.7µs  @99 25.1ms  @100
    [text_16_AA_BK] 1.8µs   @0  14.7µs  @99 25.1ms  @100

out/ok bench:samples=100 8888 filter:search=text_16_AA serial
    [text_16_AA_88] 2.35µs  @0  3.53µs  @99 16.7ms  @100
    [text_16_AA_FF] 2.09µs  @0  2.73µs  @99 2.91µs  @100
    [text_16_AA_BK] 1.75µs  @0  2.46µs  @99 2.65µs  @100
    [text_16_AA_WT] 2.1µs   @0  3.16µs  @99 3.17µs  @100

In the first "fork" case all runs are independent and have roughly
the same profile.  "thread" looks similar except you can see them
contending at the 99th percentile.  In "serial", the first bench
warms up the rest, so their 100th percentiles are all much faster.

Change-Id: I01a9f8c54b540221a9f232b271bb8ef3fda2569c
Reviewed-on: https://skia-review.googlesource.com/33585
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/BUILD.gn b/BUILD.gn
index 4f2202313b..fab0af52b0 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -1295,6 +1295,7 @@ if (skia_enable_tools) {
       "tools/ok_vias.cpp",
     ]
     deps = [
+      ":bench",
       ":gm",
       ":skia",
       ":tests",