From 680e5624e93d5c7fecb89c43478079a13b2b1bfb Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Daniel=20Mart=C3=AD?= Date: Thu, 20 May 2021 11:50:38 +0100 Subject: [PATCH] speed up tests by 20-30% by using GOGC=off See the added comment for the rationale. For that same reason, I always build Go itself via "GOGC=off ./make.bash", as it's noticeably faster. Before this change: $ go clean -cache && go test -short PASS ok mvdan.cc/garble 35.298s $ go test -short PASS ok mvdan.cc/garble 2.703s With the change: $ go clean -cache && go test -short PASS ok mvdan.cc/garble 25.323s $ go test -short PASS ok mvdan.cc/garble 2.469s Incremental test runs with a warm cache are largely unaffected, as those would run very few of those short-lived and allocation-heavy programs. However, when the build cache isn't warm (such as when garble itself is modified), we easily see savings of 20-30%. We might revisit this in the future if Go's GC gets better in these situations, which should make "go build" faster. For now, we run our tests very often, so having them burn a bit less CPU is nice. --- main_test.go | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/main_test.go b/main_test.go index 57bd449..6314126 100644 --- a/main_test.go +++ b/main_test.go @@ -58,8 +58,25 @@ func TestScripts(t *testing.T) { Dir: filepath.Join("testdata", "scripts"), Setup: func(env *testscript.Env) error { env.Vars = append(env.Vars, + // Use testdata/mod as our module proxy. "GOPROXY="+proxyURL, + + // We use our own proxy, so avoid sum.golang.org. "GONOSUMDB=*", + + // "go build" starts many short-lived Go processes, + // such as asm, buildid, compile, and link. + // They don't allocate huge amounts of memory, + // and they'll exit within seconds, + // so using the GC is basically a waste of CPU. + // Turn it off entirely, releasing memory on exit. + // + // We don't want this setting always on, + // as it could result in memory problems for users. + // But it helps for our test suite, + // as the packages are relatively small. + "GOGC=off", + "gofullversion="+runtime.Version(), )