// mutexSampleContention returns whether the current mutex operation should
// report any contention it discovers.
func mutexSampleContention() bool {
- if rate := int64(atomic.Load64(&mutexprofilerate)); rate <= 0 {
- return false
- } else {
- // TODO: have SetMutexProfileFraction do the clamping
- rate32 := uint32(rate)
- if int64(rate32) != rate {
- rate32 = ^uint32(0)
- }
- return cheaprandn(rate32) == 0
- }
+ rate := atomic.Load64(&mutexprofilerate)
+ return rate > 0 && cheaprandu64()%rate == 0
}
// unlock2Wake updates the list of Ms waiting on l, waking an M if necessary.
}
bootstrapRandReseed() // erase key we just extracted
mp.chacha8.Init64(seed)
- mp.cheaprand = rand()
+ mp.cheaprand = uint32(rand())
+ mp.cheaprand64 = rand()
}
// randn is like rand() % n but faster.
func cheaprand() uint32 {
mp := getg().m
// Implement wyrand: https://github.com/wangyi-fudan/wyhash
- // Only the platform that bits.Mul64 can be lowered
- // by the compiler should be in this list.
- if goarch.IsAmd64|goarch.IsArm64|goarch.IsPpc64|
- goarch.IsPpc64le|goarch.IsMips64|goarch.IsMips64le|
- goarch.IsS390x|goarch.IsRiscv64|goarch.IsLoong64 == 1 {
- mp.cheaprand += 0xa0761d6478bd642f
- hi, lo := bits.Mul64(mp.cheaprand, mp.cheaprand^0xe7037ed1a0b428db)
- return uint32(hi ^ lo)
+ // Only the platform that supports 64-bit multiplication
+ // natively should be allowed.
+ if bits.UintSize == 64 {
+ mp.cheaprand += 0x53c5ca59
+ hi, lo := bits.Mul32(mp.cheaprand, mp.cheaprand^0x74743c1b)
+ return hi ^ lo
}
// Implement xorshift64+: 2 32-bit xorshift sequences added together.
// Xorshift paper: https://www.jstatsoft.org/article/view/v008i14/xorshift.pdf
// This generator passes the SmallCrush suite, part of TestU01 framework:
// http://simul.iro.umontreal.ca/testu01/tu01.html
- t := (*[2]uint32)(unsafe.Pointer(&mp.cheaprand))
+ t := (*[2]uint32)(unsafe.Pointer(&mp.cheaprand64))
s1, s0 := t[0], t[1]
s1 ^= s1 << 17
s1 = s1 ^ s0 ^ s1>>7 ^ s0>>16
//go:linkname cheaprand64
//go:nosplit
func cheaprand64() int64 {
- return int64(cheaprand())<<31 ^ int64(cheaprand())
+ return int64(cheaprandu64() & ^(uint64(1) << 63))
+}
+
+// cheaprandu64 is a non-cryptographic-quality 64-bit random generator
+// suitable for calling at very high frequency (such as during sampling decisions).
+// it is "cheap" in the sense of both expense and quality.
+//
+// cheaprandu64 must not be exported to other packages:
+// the rule is that other packages using runtime-provided
+// randomness must always use rand.
+//
+//go:nosplit
+func cheaprandu64() uint64 {
+ // Implement wyrand: https://github.com/wangyi-fudan/wyhash
+ // Only the platform that bits.Mul64 can be lowered
+ // by the compiler should be in this list.
+ if goarch.IsAmd64|goarch.IsArm64|goarch.IsPpc64|
+ goarch.IsPpc64le|goarch.IsMips64|goarch.IsMips64le|
+ goarch.IsS390x|goarch.IsRiscv64|goarch.IsLoong64 == 1 {
+ mp := getg().m
+ // Implement wyrand: https://github.com/wangyi-fudan/wyhash
+ mp.cheaprand64 += 0xa0761d6478bd642f
+ hi, lo := bits.Mul64(mp.cheaprand64, mp.cheaprand64^0xe7037ed1a0b428db)
+ return hi ^ lo
+ }
+
+ return uint64(cheaprand())<<32 | uint64(cheaprand())
}
// cheaprandn is like cheaprand() % n but faster.