From c8874829a17bbc418c1af6ce200cb7cb7dd6b8af Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Dawid=20Ci=C4=99=C5=BCarkiewicz?= <dpc@dpc.pw>
Date: Sun, 6 Aug 2017 00:45:53 -0700
Subject: [PATCH] bench: Don't drop the output data

Since in the current benchmarks the output data is discarded, compiler
is smart enough to eliminate all data copying (both in to the buffer,
and out of the buffer), and roll over the original buffer only.

With this change the overhead of coping things is being measured as
well. I still wonder if both copyings are being done, or just the one
out of the buffer.

In the real code, at least the out of the buffer copying would be
unavoidable, as unless something can be done immediately with that data,
it has to be copied somewhere, eg. to send for processing to another
thread.
---
 chunking/benches/all.rs | 17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/chunking/benches/all.rs b/chunking/benches/all.rs
index 79b2fb9..9f28604 100644
--- a/chunking/benches/all.rs
+++ b/chunking/benches/all.rs
@@ -26,22 +26,21 @@ fn random_data(seed: u64, size: usize) -> Vec<u8> {
 }
 
 
-struct CutPositions(Vec<u64>, u64);
+struct CutPositions(Vec<u8>, u64);
 
 impl CutPositions {
     pub fn new() -> Self {
-        CutPositions(vec![], 0)
+        CutPositions(Vec::with_capacity(1024*1024), 0)
     }
 
-    pub fn positions(&self) -> &[u64] {
+    pub fn data(&self) -> &[u8] {
         &self.0
     }
 }
 
 impl Write for CutPositions {
     fn write(&mut self, data: &[u8]) -> Result<usize, io::Error> {
-        self.1 += data.len() as u64;
-        self.0.push(self.1);
+        self.0.extend_from_slice(data);
         Ok(data.len())
     }
 
@@ -67,7 +66,7 @@ fn test_fixed_8192(b: &mut Bencher) {
         let mut cursor = Cursor::new(&data);
         let mut sink = CutPositions::new();
         while chunker.chunk(&mut cursor, &mut sink).unwrap() == ChunkerStatus::Continue {};
-        test::black_box(sink.positions().len())
+        test::black_box(sink.data().len())
     })
 }
 
@@ -88,7 +87,7 @@ fn test_ae_8192(b: &mut Bencher) {
         let mut cursor = Cursor::new(&data);
         let mut sink = CutPositions::new();
         while chunker.chunk(&mut cursor, &mut sink).unwrap() == ChunkerStatus::Continue {};
-        test::black_box(sink.positions().len())
+        test::black_box(sink.data().len())
     })
 }
 
@@ -109,7 +108,7 @@ fn test_rabin_8192(b: &mut Bencher) {
         let mut cursor = Cursor::new(&data);
         let mut sink = CutPositions::new();
         while chunker.chunk(&mut cursor, &mut sink).unwrap() == ChunkerStatus::Continue {};
-        test::black_box(sink.positions().len())
+        test::black_box(sink.data().len())
     })
 }
 
@@ -130,6 +129,6 @@ fn test_fastcdc_8192(b: &mut Bencher) {
         let mut cursor = Cursor::new(&data);
         let mut sink = CutPositions::new();
         while chunker.chunk(&mut cursor, &mut sink).unwrap() == ChunkerStatus::Continue {};
-        test::black_box(sink.positions().len())
+        test::black_box(sink.data().len())
     })
 }