When you have data races the results are undefined.
$ go version
go version devel +dd81c37 Sat Jul 15 05:43:45 2017 +0000 linux/amd64
$ go test -race -run=! -bench=. -benchmem -cpu=1,2,4,8 pubsub_test.go
==================
WARNING: DATA RACE
Read at 0x00c4200140c0 by goroutine 18:
command-line-arguments.BenchmarkPubSubPrimitiveChannelsMultiple()
/home/peter/gopath/src/nuts/pubsub_test.go:59 +0x51d
testing.(*B).runN()
/home/peter/go/src/testing/benchmark.go:141 +0x12a
testing.(*B).run1.func1()
/home/peter/go/src/testing/benchmark.go:214 +0x6b
Previous write at 0x00c4200140c0 by goroutine 57:
[failed to restore the stack]
Goroutine 18 (running) created at:
testing.(*B).run1()
/home/peter/go/src/testing/benchmark.go:207 +0x8c
testing.(*B).Run()
/home/peter/go/src/testing/benchmark.go:513 +0x482
testing.runBenchmarks.func1()
/home/peter/go/src/testing/benchmark.go:417 +0xa7
testing.(*B).runN()
/home/peter/go/src/testing/benchmark.go:141 +0x12a
testing.runBenchmarks()
/home/peter/go/src/testing/benchmark.go:423 +0x86d
testing.(*M).Run()
/home/peter/go/src/testing/testing.go:928 +0x51e
main.main()
command-line-arguments/_test/_testmain.go:46 +0x1d3
Goroutine 57 (finished) created at:
command-line-arguments.BenchmarkPubSubPrimitiveChannelsMultiple()
/home/peter/gopath/src/nuts/pubsub_test.go:40 +0x290
testing.(*B).runN()
/home/peter/go/src/testing/benchmark.go:141 +0x12a
testing.(*B).run1.func1()
/home/peter/go/src/testing/benchmark.go:214 +0x6b
==================
--- FAIL: BenchmarkPubSubPrimitiveChannelsMultiple
benchmark.go:147: race detected during execution of benchmark
==================
WARNING: DATA RACE
Read at 0x00c42000c030 by goroutine 1079:
command-line-arguments.BenchmarkPubSubWaitGroupMultiple.func1()
/home/peter/gopath/src/nuts/pubsub_test.go:76 +0x9e
Previous write at 0x00c42000c030 by goroutine 7:
command-line-arguments.BenchmarkPubSubWaitGroupMultiple()
/home/peter/gopath/src/nuts/pubsub_test.go:101 +0x475
testing.(*B).runN()
/home/peter/go/src/testing/benchmark.go:141 +0x12a
testing.(*B).run1.func1()
/home/peter/go/src/testing/benchmark.go:214 +0x6b
Goroutine 1079 (running) created at:
command-line-arguments.BenchmarkPubSubWaitGroupMultiple()
/home/peter/gopath/src/nuts/pubsub_test.go:93 +0x2e6
testing.(*B).runN()
/home/peter/go/src/testing/benchmark.go:141 +0x12a
testing.(*B).run1.func1()
/home/peter/go/src/testing/benchmark.go:214 +0x6b
Goroutine 7 (running) created at:
testing.(*B).run1()
/home/peter/go/src/testing/benchmark.go:207 +0x8c
testing.(*B).Run()
/home/peter/go/src/testing/benchmark.go:513 +0x482
testing.runBenchmarks.func1()
/home/peter/go/src/testing/benchmark.go:417 +0xa7
testing.(*B).runN()
/home/peter/go/src/testing/benchmark.go:141 +0x12a
testing.runBenchmarks()
/home/peter/go/src/testing/benchmark.go:423 +0x86d
testing.(*M).Run()
/home/peter/go/src/testing/testing.go:928 +0x51e
main.main()
command-line-arguments/_test/_testmain.go:46 +0x1d3
==================
==================
WARNING: DATA RACE
Write at 0x00c42000c030 by goroutine 7:
command-line-arguments.BenchmarkPubSubWaitGroupMultiple()
/home/peter/gopath/src/nuts/pubsub_test.go:101 +0x475
testing.(*B).runN()
/home/peter/go/src/testing/benchmark.go:141 +0x12a
testing.(*B).run1.func1()
/home/peter/go/src/testing/benchmark.go:214 +0x6b
Previous read at 0x00c42000c030 by goroutine 1078:
command-line-arguments.BenchmarkPubSubWaitGroupMultiple.func1()
/home/peter/gopath/src/nuts/pubsub_test.go:76 +0x9e
Goroutine 7 (running) created at:
testing.(*B).run1()
/home/peter/go/src/testing/benchmark.go:207 +0x8c
testing.(*B).Run()
/home/peter/go/src/testing/benchmark.go:513 +0x482
testing.runBenchmarks.func1()
/home/peter/go/src/testing/benchmark.go:417 +0xa7
testing.(*B).runN()
/home/peter/go/src/testing/benchmark.go:141 +0x12a
testing.runBenchmarks()
/home/peter/go/src/testing/benchmark.go:423 +0x86d
testing.(*M).Run()
/home/peter/go/src/testing/testing.go:928 +0x51e
main.main()
command-line-arguments/_test/_testmain.go:46 +0x1d3
Goroutine 1078 (running) created at:
command-line-arguments.BenchmarkPubSubWaitGroupMultiple()
/home/peter/gopath/src/nuts/pubsub_test.go:93 +0x2e6
testing.(*B).runN()
/home/peter/go/src/testing/benchmark.go:141 +0x12a
testing.(*B).run1.func1()
/home/peter/go/src/testing/benchmark.go:214 +0x6b
==================
==================
WARNING: DATA RACE
Read at 0x00c4200140c8 by goroutine 7:
command-line-arguments.BenchmarkPubSubWaitGroupMultiple()
/home/peter/gopath/src/nuts/pubsub_test.go:109 +0x51d
testing.(*B).runN()
/home/peter/go/src/testing/benchmark.go:141 +0x12a
testing.(*B).run1.func1()
/home/peter/go/src/testing/benchmark.go:214 +0x6b
Previous write at 0x00c4200140c8 by goroutine 175:
sync/atomic.AddInt64()
/home/peter/go/src/runtime/race_amd64.s:276 +0xb
command-line-arguments.BenchmarkPubSubWaitGroupMultiple.func1()
/home/peter/gopath/src/nuts/pubsub_test.go:88 +0x19a
Goroutine 7 (running) created at:
testing.(*B).run1()
/home/peter/go/src/testing/benchmark.go:207 +0x8c
testing.(*B).Run()
/home/peter/go/src/testing/benchmark.go:513 +0x482
testing.runBenchmarks.func1()
/home/peter/go/src/testing/benchmark.go:417 +0xa7
testing.(*B).runN()
/home/peter/go/src/testing/benchmark.go:141 +0x12a
testing.runBenchmarks()
/home/peter/go/src/testing/benchmark.go:423 +0x86d
testing.(*M).Run()
/home/peter/go/src/testing/testing.go:928 +0x51e
main.main()
command-line-arguments/_test/_testmain.go:46 +0x1d3
Goroutine 175 (finished) created at:
command-line-arguments.BenchmarkPubSubWaitGroupMultiple()
/home/peter/gopath/src/nuts/pubsub_test.go:93 +0x2e6
testing.(*B).runN()
/home/peter/go/src/testing/benchmark.go:141 +0x12a
testing.(*B).run1.func1()
/home/peter/go/src/testing/benchmark.go:214 +0x6b
==================
--- FAIL: BenchmarkPubSubWaitGroupMultiple
benchmark.go:147: race detected during execution of benchmark
FAIL
exit status 1
FAIL command-line-arguments 0.726s
$
Peter
On Sunday, July 16, 2017 at 10:20:21 AM UTC-4, Zohaib Sibte Hassan wrote:
>
> I have been spending my day over implementing an efficient PubSub system.
> I had implemented one before using channels, and I wanted to benchmark that
> against sync.Cond. Here is the quick and dirty test that I put together
> https://gist.github.com/maxpert/f3c405c516ba2d4c8aa8b0695e0e054e. Now my
> confusion starts when I change GOMAXPROCS to test how it would perform on
> my age old Raspberry Pi. Here are results:
>
> mxp@carbon:~/repos/raspchat/src/sibte.so/rascore$ GOMAXPROCS=8 go test
> -run none -bench Multiple -cpuprofile=cpu.out -memprofile=mem.out -benchmem
> BenchmarkPubSubPrimitiveChannelsMultiple-8 10000 165419 ns/op
> 92 B/op 2 allocs/op
> BenchmarkPubSubWaitGroupMultiple-8 10000 204685 ns/op
> 53 B/op 2 allocs/op
> PASS
> ok sibte.so/rascore 3.749s
> mxp@carbon:~/repos/raspchat/src/sibte.so/rascore$ GOMAXPROCS=4 go test
> -run none -bench Multiple -cpuprofile=cpu.out -memprofile=mem.out -benchmem
> BenchmarkPubSubPrimitiveChannelsMultiple-4 20000 101704 ns/op
> 60 B/op 2 allocs/op
> BenchmarkPubSubWaitGroupMultiple-4 10000 204039 ns/op
> 52 B/op 2 allocs/op
> PASS
> ok sibte.so/rascore 5.087s
> mxp@carbon:~/repos/raspchat/src/sibte.so/rascore$ GOMAXPROCS=2 go test
> -run none -bench Multiple -cpuprofile=cpu.out -memprofile=mem.out -benchmem
> BenchmarkPubSubPrimitiveChannelsMultiple-2 30000 51255 ns/op
> 54 B/op 2 allocs/op
> BenchmarkPubSubWaitGroupMultiple-2 20000 60871 ns/op
> 43 B/op 2 allocs/op
> PASS
> ok sibte.so/rascore 4.022s
> mxp@carbon:~/repos/raspchat/src/sibte.so/rascore$ GOMAXPROCS=1 go test
> -run none -bench Multiple -cpuprofile=cpu.out -memprofile=mem.out -benchmem
> BenchmarkPubSubPrimitiveChannelsMultiple 20000 79534 ns/op 61
> B/op 2 allocs/op
> BenchmarkPubSubWaitGroupMultiple 100000 19066 ns/op 40
> B/op 2 allocs/op
> PASS
> ok sibte.so/rascore 4.502s
>
> I tried multiple times and results are consistent. I am using Go 1.8,
> Linux x64, 8GB RAM. I have multiple questions:
>
>
> - Why do channels perform worst than sync.Cond in single core results?
> Context switching is same if anything it should perform worst.
> - As I increase the max procs the sync.Cond results go down which
> might be explainable, but what is up with channels? 20k to 30k to 20k to
> 10k :( I have a i5 with 4 cores, so it should have peaked at 4 procs
> (pst.
> I tried 3 as well it's consistent).
>
> I am still suspicious I am not making some kind of mistake in code. Any
> ideas?
>
> - Thanks
>
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