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For certain values of GOMAXPROCS, the current code is less random than it looks. For example with GOMAXPROCS=12, there are 4 coprimes: 1 5 7 11. That's bad, as 12 and 4 are not relatively prime. So if pos == 2, then we always pick 7 as the inc. We want to pick pos and inc independently at random. Change-Id: I5c7e4f01f9223cbc2db12a685dc0bced2cf39abf Reviewed-on: https://go-review.googlesource.com/c/go/+/369976 Run-TryBot: Keith Randall <khr@golang.org> Trust: Keith Randall <khr@golang.org> TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
51 lines
1.4 KiB
Go
51 lines
1.4 KiB
Go
// Copyright 2016 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Proc unit tests. In runtime package so can use runtime guts.
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package runtime
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func RunStealOrderTest() {
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var ord randomOrder
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for procs := 1; procs <= 64; procs++ {
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ord.reset(uint32(procs))
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if procs >= 3 && len(ord.coprimes) < 2 {
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panic("too few coprimes")
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}
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for co := 0; co < len(ord.coprimes); co++ {
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enum := ord.start(uint32(co))
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checked := make([]bool, procs)
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for p := 0; p < procs; p++ {
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x := enum.position()
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if checked[x] {
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println("procs:", procs, "inc:", enum.inc)
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panic("duplicate during enumeration")
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}
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checked[x] = true
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enum.next()
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}
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if !enum.done() {
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panic("not done")
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}
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}
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}
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// Make sure that different arguments to ord.start don't generate the
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// same pos+inc twice.
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for procs := 2; procs <= 64; procs++ {
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ord.reset(uint32(procs))
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checked := make([]bool, procs*procs)
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// We want at least procs*len(ord.coprimes) different pos+inc values
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// before we start repeating.
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for i := 0; i < procs*len(ord.coprimes); i++ {
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enum := ord.start(uint32(i))
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j := enum.pos*uint32(procs) + enum.inc
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if checked[j] {
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println("procs:", procs, "pos:", enum.pos, "inc:", enum.inc)
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panic("duplicate pos+inc during enumeration")
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}
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checked[j] = true
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}
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}
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}
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