x/perf/benchstat: no group headers shown if only one group

[shawndx]

What version of Go are you using (go version)?

$ go version
go version devel +a6a7b148f8 Mon Jul 15 23:00:52 2019 +0000 linux/amd64

Does this issue reproduce with the latest release?

Yes.

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/xiaji01/.cache/go-build"
GOENV="/home/xiaji01/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/xiaji01/.go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/mnt/share/homes/xiaji01/go1.12/x86"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/mnt/share/homes/xiaji01/go1.12/x86/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build378631038=/tmp/go-build -gno-record-gcc-switches"

What did you do?

#install benchstat
go get -d golang.org/x/perf/cmd/benchstat
go install golang.org/x/perf/cmd/benchstat

#run benchmark of a SINGLE package under /src
go test -count 5 -timeout 20m -run=^$ -bench=. crypto/sha256 | tee bench.log

#run benchstat to do analysis, using default options
benchstat bench.log

#output of the benchstat doesn't have group header (pkg, goos, goarch)
name time/op
Hash8Bytes-40 294ns ± 3%
Hash1K-40 3.50µs ± 5%
Hash8K-40 26.2µs ± 4%

name speed
Hash8Bytes-40 27.2MB/s ± 3%
Hash1K-40 293MB/s ± 4%
Hash8K-40 313MB/s ± 4%

What did you expect to see?

Expect benchstat to output group header even the benchmarking data only contains one group.
Since there are a few Go benchmarks from different packages sharing the same name, for example, both crypto/sha256 and crypto/sha512 have benchmarks "BenchmarkHash8Bytes", "BenchmarkHash1K", etc., having a package name, which is part of the group header by default, would facilitate recording their performance data in a database.

We can fulfill the above requirement via multiple ways, just wondering if having benchstat support it is a better option.

The restriction was introduced in commit add18dd,

•                           if len(c.Groups) > 1 {
  

•                                   // Show group headers if there is more than one group.
  

•                                   row.Group = key.Group
  

Any comment is highly appreciated.

Attaching two benchmark log files for your reference.

bench_one_pkg.log: benchmark log of package crypto/sha256, benchstat's output has no group

bench_two_pkgs.log: benchmark log of packages crypto/sha256 and crypto/sha512, benchstat's output has groups.
bench_one_pkg.log
bench_two_pkgs.log

What did you see instead?

[katiehockman]

/cc @rsc

[katiehockman]

/cc @aclements

[gopherbot]

Change https://golang.org/cl/309969 mentions this issue: cmd/benchstat: new version of benchstat