index: don't log in benchmark, even to ioutil.Discard. just a CPU distraction.

Change-Id: Id4d8b761cd81a7c8abd7e21d139bffc818aff5e1

pkg/index/corpus.go

@@ -140,13 +140,13 @@ func (c *Corpus) scanFromStorage(s sorted.KeyValue) error {
 	var ms0 *runtime.MemStats
 	if logCorpusStats {
 		ms0 = memstats()
-	}
 		log.Printf("Slurping corpus to memory from index...")
+		log.Printf("Slurping corpus to memory from index... (1/6: meta rows)")
+	}
 
 	// We do the "meta" rows first, before the prefixes below, because it
 	// populates the blobs map (used for blobref interning) and the camBlobs
 	// map (used for hinting the size of other maps)
-	log.Printf("Slurping corpus to memory from index... (1/6: meta rows)")
 	if err := c.scanPrefix(s, "meta:"); err != nil {
 		return err
 	}
@@ -162,7 +162,9 @@ func (c *Corpus) scanFromStorage(s sorted.KeyValue) error {
 		"imagesize|",
 	}
 	for i, prefix := range prefixes {
+		if logCorpusStats {
 			log.Printf("Slurping corpus to memory from index... (%d/%d: prefix %q)", i+2, len(prefixes)+1, prefix)
+		}
 		if err := c.scanPrefix(s, prefix); err != nil {
 			return err
 		}

pkg/index/corpus_bench_test.go

@@ -18,8 +18,6 @@ package index_test
 
 import (
 	"fmt"
-	"io/ioutil"
-	"log"
 	"sync"
 	"testing"
 	"time"
@@ -58,9 +56,5 @@ func BenchmarkCorpusFromStorage(b *testing.B) {
 		if err != nil {
 			b.Fatal(err)
 		}
-		if i == 0 {
-			// Only worth logging any failures in the first round.
-			log.SetOutput(ioutil.Discard)
-		}
 	}
 }