From ecb2f231fa41b581319505139f8d5ac779763bee Mon Sep 17 00:00:00 2001 From: Meng Zhuo Date: Thu, 30 Sep 2021 22:46:09 +0800 Subject: runtime,sync: using fastrandn instead of modulo reduction MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit fastrandn is ~50% faster than fastrand() % n. `ack -v 'fastrand\(\)\s?\%'` finds all modulo on fastrand() name old time/op new time/op delta Fastrandn/2 2.86ns ± 0% 1.59ns ± 0% -44.35% (p=0.000 n=9+10) Fastrandn/3 2.87ns ± 1% 1.59ns ± 0% -44.41% (p=0.000 n=10+9) Fastrandn/4 2.87ns ± 1% 1.58ns ± 1% -45.10% (p=0.000 n=10+10) Fastrandn/5 2.86ns ± 1% 1.58ns ± 1% -44.84% (p=0.000 n=10+10) Change-Id: Ic91f5ca9b9e3b65127bc34792b62fd64fbd13b5c Reviewed-on: https://go-review.googlesource.com/c/go/+/353269 Trust: Meng Zhuo Run-TryBot: Meng Zhuo TryBot-Result: Go Bot Reviewed-by: Keith Randall --- src/runtime/malloc.go | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'src/runtime/malloc.go') diff --git a/src/runtime/malloc.go b/src/runtime/malloc.go index 7affe244a2..c389cb1e45 100644 --- a/src/runtime/malloc.go +++ b/src/runtime/malloc.go @@ -1301,7 +1301,7 @@ func fastexprand(mean int) int32 { // x = -log_e(q) * mean // x = log_2(q) * (-log_e(2)) * mean ; Using log_2 for efficiency const randomBitCount = 26 - q := fastrand()%(1< 0 { qlog = 0 @@ -1319,7 +1319,7 @@ func nextSampleNoFP() uintptr { rate = 0x3fffffff } if rate != 0 { - return uintptr(fastrand() % uint32(2*rate)) + return uintptr(fastrandn(uint32(2 * rate))) } return 0 } -- cgit v1.3-5-g9baa