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runtime: remove VDSO fallback test and benchmarks

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These tests assume that it is OK to switch between time implementations,
but the clock_gettime call uses CLOCK_MONOTONIC and the fallback call,
gettimeofday, uses CLOCK_REALTIME. Disabling the clock_gettime call means
that calls to nanotime will start returning very different values.
This breaks the new timer code, which assumes that nanotime will return
a consistently increasing value.

This test is not very useful in any case as it doesn't check the results.

Removing this file also removes BenchmarkTimeNow, which is a duplicate
of BenchmarkNow in the time package.

Updates #27707
Fixes #32109

Change-Id: I6a884af07f75822d724193c5eed94742f524f07d
Reviewed-on: https://go-review.googlesource.com/c/go/+/174679
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
This commit is contained in:
Ian Lance Taylor 2019-04-30 21:06:01 -07:00
parent d97bd5d07a
commit 1531192272
1 changed files with 0 additions and 63 deletions
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63
src/runtime/vdso_linux_test.go
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@ -1,63 +0,0 @@
// Copyright 2017 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// +build linux
// +build 386 amd64 arm arm64 ppc64 ppc64le
package runtime_test
import (
"testing"
"time"
_ "unsafe"
)
// These tests are a little risky because they overwrite the vdsoClockgettimeSym value.
// It's normally initialized at startup and remains unchanged after that.
//go:linkname vdsoClockgettimeSym runtime.vdsoClockgettimeSym
var vdsoClockgettimeSym uintptr
func TestClockVDSOAndFallbackPaths(t *testing.T) {
// Check that we can call walltime() and nanotime() with and without their (1st) fast-paths.
// This just checks that fast and fallback paths can be called, rather than testing their
// results.
//
// Call them indirectly via time.Now(), so we don't need auxiliary .s files to allow us to
// use go:linkname to refer to the functions directly.
save := vdsoClockgettimeSym
if save == 0 {
t.Log("vdsoClockgettime symbol not found; fallback path will be used by default")
}
// Call with fast-path enabled (if vDSO symbol found at startup)
time.Now()
// Call with fast-path disabled
vdsoClockgettimeSym = 0
time.Now()
vdsoClockgettimeSym = save
}
func BenchmarkClockVDSOAndFallbackPaths(b *testing.B) {
run := func(b *testing.B) {
for i := 0; i < b.N; i++ {
// Call via time.Now() - see comment in test above.
time.Now()
}
}
save := vdsoClockgettimeSym
b.Run("vDSO", run)
vdsoClockgettimeSym = 0
b.Run("Fallback", run)
vdsoClockgettimeSym = save
}
func BenchmarkTimeNow(b *testing.B) {
for i := 0; i < b.N; i++ {
time.Now()
}
}