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authorCarlo Alberto Ferraris <cafxx@strayorange.com>2022-07-22 14:18:33 +0900
committerGopher Robot <gobot@golang.org>2022-09-27 16:55:15 +0000
commitdcb90152a444be97fcc45bb12d176641c1b0d90e (patch)
treedf36eade7b0ce24cc0988cf248b6f9bd8a0f4f54 /src/strings
parent7d157fd0eb637a4c58f629421dd8d028022391d2 (diff)
downloadgo-git-dcb90152a444be97fcc45bb12d176641c1b0d90e.tar.gz
bytes,strings: optimize Repeat
When generating long strings or slices with Repeat we currently reuse intermediate states as a way to quickly build exponentially longer results. This works well as long as the intermediate states fit into the processor D-cache. If they don't we start thrashing the D-cache by reading in the whole intermediate state over and over on each iteration. Instead, once we reach a large enough intermediate state (that allows the memcpy operation to perform at peak) we cap the size of chunk of the state that is used as source for subsequent appends. This ensures that this smaller source chunk is always present in the D-cache, and the append operation does not need to read the state contents from memory. Currently the cap is set to 8KB, a number derived via experimentation to yield the highest performance across a a large range of result sizes. Slightly higher caps also produced similar results: 8KB was chosen as the smallest one in this performance plateau with the intention to minimize D-cache pollution. For result sizes larger than the fastest cache levels we get significantly higher performance compared to the current implementation: strings: name old speed new speed delta RepeatLarge/256/1-16 1.73GB/s ± 1% 1.73GB/s ± 0% ~ (p=0.556 n=5+4) RepeatLarge/256/16-16 2.02GB/s ± 0% 1.95GB/s ± 8% ~ (p=0.222 n=5+5) RepeatLarge/512/1-16 2.30GB/s ±13% 2.47GB/s ± 1% ~ (p=0.548 n=5+5) RepeatLarge/512/16-16 2.38GB/s ±16% 2.77GB/s ± 1% +16.27% (p=0.032 n=5+5) RepeatLarge/1024/1-16 3.17GB/s ± 1% 3.18GB/s ± 0% ~ (p=0.730 n=4+5) RepeatLarge/1024/16-16 3.39GB/s ± 2% 3.38GB/s ± 1% ~ (p=0.548 n=5+5) RepeatLarge/2048/1-16 3.32GB/s ± 2% 3.32GB/s ± 2% ~ (p=1.000 n=5+5) RepeatLarge/2048/16-16 3.41GB/s ± 4% 3.46GB/s ± 2% ~ (p=0.310 n=5+5) RepeatLarge/4096/1-16 3.60GB/s ± 4% 3.67GB/s ± 3% ~ (p=0.690 n=5+5) RepeatLarge/4096/16-16 3.74GB/s ± 3% 3.71GB/s ± 5% ~ (p=0.690 n=5+5) RepeatLarge/8192/1-16 3.94GB/s ± 4% 4.01GB/s ± 1% ~ (p=0.222 n=5+5) RepeatLarge/8192/16-16 3.94GB/s ± 6% 4.05GB/s ± 1% ~ (p=0.222 n=5+5) RepeatLarge/8192/4097-16 4.25GB/s ± 6% 4.32GB/s ± 3% ~ (p=0.690 n=5+5) RepeatLarge/16384/1-16 4.96GB/s ± 1% 5.02GB/s ± 2% ~ (p=0.421 n=5+5) RepeatLarge/16384/16-16 4.99GB/s ± 2% 5.07GB/s ± 1% ~ (p=0.421 n=5+5) RepeatLarge/16384/4097-16 5.15GB/s ± 3% 5.17GB/s ± 1% ~ (p=1.000 n=5+5) RepeatLarge/32768/1-16 5.44GB/s ± 2% 5.42GB/s ± 1% ~ (p=0.841 n=5+5) RepeatLarge/32768/16-16 5.46GB/s ± 4% 5.44GB/s ± 1% ~ (p=0.905 n=5+4) RepeatLarge/32768/4097-16 4.84GB/s ± 2% 4.59GB/s ±12% -5.05% (p=0.032 n=5+5) RepeatLarge/65536/1-16 5.85GB/s ± 0% 5.84GB/s ± 1% ~ (p=0.690 n=5+5) RepeatLarge/65536/16-16 5.81GB/s ± 2% 5.84GB/s ± 2% ~ (p=0.421 n=5+5) RepeatLarge/65536/4097-16 5.38GB/s ± 6% 5.45GB/s ± 1% ~ (p=1.000 n=5+5) RepeatLarge/131072/1-16 6.20GB/s ± 1% 6.31GB/s ± 1% +1.80% (p=0.008 n=5+5) RepeatLarge/131072/16-16 6.12GB/s ± 3% 6.25GB/s ± 3% ~ (p=0.095 n=5+5) RepeatLarge/131072/4097-16 5.95GB/s ± 1% 5.85GB/s ±10% ~ (p=1.000 n=5+5) RepeatLarge/262144/1-16 6.33GB/s ± 1% 6.56GB/s ± 0% +3.62% (p=0.016 n=5+4) RepeatLarge/262144/16-16 6.42GB/s ± 0% 6.65GB/s ± 1% +3.58% (p=0.016 n=4+5) RepeatLarge/262144/4097-16 6.31GB/s ± 1% 6.44GB/s ± 1% +1.94% (p=0.008 n=5+5) RepeatLarge/524288/1-16 6.23GB/s ± 1% 6.92GB/s ± 3% +11.02% (p=0.008 n=5+5) RepeatLarge/524288/16-16 6.24GB/s ± 1% 6.97GB/s ± 2% +11.77% (p=0.016 n=4+5) RepeatLarge/524288/4097-16 6.14GB/s ± 2% 6.73GB/s ± 3% +9.50% (p=0.008 n=5+5) RepeatLarge/1048576/1-16 5.23GB/s ± 1% 6.53GB/s ± 6% +24.85% (p=0.008 n=5+5) RepeatLarge/1048576/16-16 5.21GB/s ± 1% 6.56GB/s ± 4% +25.93% (p=0.008 n=5+5) RepeatLarge/1048576/4097-16 5.22GB/s ± 1% 6.26GB/s ± 2% +20.09% (p=0.008 n=5+5) RepeatLarge/2097152/1-16 3.95GB/s ± 1% 5.96GB/s ± 1% +51.01% (p=0.008 n=5+5) RepeatLarge/2097152/16-16 3.94GB/s ± 1% 5.98GB/s ± 2% +51.99% (p=0.008 n=5+5) RepeatLarge/2097152/4097-16 4.94GB/s ± 1% 5.71GB/s ± 2% +15.63% (p=0.008 n=5+5) RepeatLarge/4194304/1-16 3.10GB/s ± 1% 5.89GB/s ± 1% +89.90% (p=0.008 n=5+5) RepeatLarge/4194304/16-16 3.09GB/s ± 1% 5.86GB/s ± 1% +89.89% (p=0.008 n=5+5) RepeatLarge/4194304/4097-16 3.13GB/s ± 1% 5.89GB/s ± 1% +88.36% (p=0.008 n=5+5) RepeatLarge/8388608/1-16 3.06GB/s ± 1% 6.31GB/s ±16% +105.84% (p=0.008 n=5+5) RepeatLarge/8388608/16-16 3.08GB/s ± 1% 6.62GB/s ± 1% +114.66% (p=0.008 n=5+5) RepeatLarge/8388608/4097-16 3.13GB/s ± 2% 6.87GB/s ± 1% +119.62% (p=0.008 n=5+5) RepeatLarge/16777216/1-16 3.21GB/s ± 3% 5.88GB/s ± 1% +83.27% (p=0.008 n=5+5) RepeatLarge/16777216/16-16 3.23GB/s ± 2% 5.84GB/s ± 2% +80.49% (p=0.008 n=5+5) RepeatLarge/16777216/4097-16 3.30GB/s ± 6% 5.88GB/s ± 2% +78.18% (p=0.008 n=5+5) RepeatLarge/33554432/1-16 3.71GB/s ± 3% 5.91GB/s ± 2% +59.17% (p=0.008 n=5+5) RepeatLarge/33554432/16-16 3.67GB/s ± 3% 5.91GB/s ± 2% +61.13% (p=0.008 n=5+5) RepeatLarge/33554432/4097-16 3.71GB/s ± 1% 5.77GB/s ± 6% +55.51% (p=0.008 n=5+5) RepeatLarge/67108864/1-16 4.61GB/s ±11% 6.00GB/s ± 5% +30.15% (p=0.008 n=5+5) RepeatLarge/67108864/16-16 4.62GB/s ± 7% 6.11GB/s ± 2% +32.35% (p=0.008 n=5+5) RepeatLarge/67108864/4097-16 4.71GB/s ± 2% 6.24GB/s ± 2% +32.60% (p=0.008 n=5+5) RepeatLarge/134217728/1-16 4.53GB/s ± 8% 6.28GB/s ±11% +38.57% (p=0.008 n=5+5) RepeatLarge/134217728/16-16 4.78GB/s ± 3% 6.36GB/s ± 3% +33.16% (p=0.008 n=5+5) RepeatLarge/134217728/4097-16 4.73GB/s ± 6% 6.46GB/s ± 3% +36.63% (p=0.008 n=5+5) RepeatLarge/268435456/1-16 4.09GB/s ±25% 6.37GB/s ±19% +56.00% (p=0.008 n=5+5) RepeatLarge/268435456/16-16 4.50GB/s ± 4% 6.86GB/s ± 0% +52.49% (p=0.016 n=5+4) RepeatLarge/268435456/4097-16 4.73GB/s ± 5% 6.90GB/s ± 0% +45.94% (p=0.008 n=5+5) RepeatLarge/536870912/1-16 4.38GB/s ±36% 6.52GB/s ± 8% +48.68% (p=0.008 n=5+5) RepeatLarge/536870912/16-16 4.69GB/s ±12% 6.90GB/s ± 1% +46.97% (p=0.008 n=5+5) RepeatLarge/536870912/4097-16 4.87GB/s ± 8% 6.98GB/s ± 0% +43.36% (p=0.008 n=5+5) RepeatLarge/1073741824/1-16 3.87GB/s ±28% 6.96GB/s ± 1% +79.94% (p=0.016 n=5+4) RepeatLarge/1073741824/16-16 4.79GB/s ± 9% 6.93GB/s ± 0% +44.79% (p=0.008 n=5+5) RepeatLarge/1073741824/4097-16 4.65GB/s ± 8% 7.02GB/s ± 1% +51.02% (p=0.008 n=5+5) bytes: name old speed new speed delta RepeatLarge/256/1-16 1.93GB/s ± 1% 1.84GB/s ± 1% -4.81% (p=0.000 n=10+10) RepeatLarge/256/16-16 2.25GB/s ± 2% 2.15GB/s ± 1% -4.45% (p=0.000 n=9+8) RepeatLarge/512/1-16 2.71GB/s ± 1% 2.62GB/s ± 1% -3.27% (p=0.000 n=10+9) RepeatLarge/512/16-16 2.96GB/s ± 4% 2.91GB/s ± 1% ~ (p=0.243 n=9+10) RepeatLarge/1024/1-16 3.35GB/s ± 1% 3.27GB/s ± 1% -2.61% (p=0.000 n=9+10) RepeatLarge/1024/16-16 3.56GB/s ± 2% 3.52GB/s ± 1% -1.10% (p=0.010 n=10+9) RepeatLarge/2048/1-16 3.52GB/s ± 1% 3.45GB/s ± 1% -1.92% (p=0.000 n=10+10) RepeatLarge/2048/16-16 3.61GB/s ± 1% 3.58GB/s ± 0% -0.82% (p=0.008 n=9+8) RepeatLarge/4096/1-16 3.85GB/s ± 2% 3.80GB/s ± 2% ~ (p=0.165 n=10+10) RepeatLarge/4096/16-16 3.88GB/s ± 3% 3.84GB/s ± 4% ~ (p=0.393 n=10+10) RepeatLarge/8192/1-16 4.12GB/s ± 2% 4.04GB/s ± 1% -1.96% (p=0.000 n=10+10) RepeatLarge/8192/16-16 4.11GB/s ± 2% 4.09GB/s ± 1% ~ (p=0.278 n=9+10) RepeatLarge/8192/4097-16 4.38GB/s ± 1% 4.39GB/s ± 4% ~ (p=0.720 n=9+10) RepeatLarge/16384/1-16 5.06GB/s ± 2% 4.95GB/s ± 3% -2.29% (p=0.001 n=10+9) RepeatLarge/16384/16-16 5.11GB/s ± 3% 5.06GB/s ± 3% ~ (p=0.315 n=10+9) RepeatLarge/16384/4097-16 5.22GB/s ± 3% 5.26GB/s ± 3% ~ (p=0.211 n=9+10) RepeatLarge/32768/1-16 5.54GB/s ± 2% 5.50GB/s ± 3% ~ (p=0.353 n=10+10) RepeatLarge/32768/16-16 5.55GB/s ± 1% 5.60GB/s ± 1% +0.91% (p=0.035 n=10+9) RepeatLarge/32768/4097-16 4.88GB/s ± 2% 4.85GB/s ± 2% ~ (p=0.447 n=10+9) RepeatLarge/65536/1-16 5.86GB/s ± 1% 5.93GB/s ± 2% +1.18% (p=0.043 n=8+10) RepeatLarge/65536/16-16 5.83GB/s ± 2% 5.98GB/s ± 1% +2.67% (p=0.000 n=10+10) RepeatLarge/65536/4097-16 5.57GB/s ± 0% 5.56GB/s ± 3% ~ (p=0.696 n=8+10) RepeatLarge/131072/1-16 6.23GB/s ± 1% 6.38GB/s ± 2% +2.51% (p=0.000 n=9+10) RepeatLarge/131072/16-16 6.21GB/s ± 2% 6.37GB/s ± 1% +2.72% (p=0.000 n=9+10) RepeatLarge/131072/4097-16 6.04GB/s ± 1% 6.09GB/s ± 3% ~ (p=0.356 n=9+10) RepeatLarge/262144/1-16 6.47GB/s ± 1% 6.63GB/s ± 2% +2.57% (p=0.003 n=10+10) RepeatLarge/262144/16-16 6.45GB/s ± 2% 6.69GB/s ± 2% +3.65% (p=0.000 n=10+10) RepeatLarge/262144/4097-16 6.35GB/s ± 1% 6.51GB/s ± 2% +2.48% (p=0.000 n=9+10) RepeatLarge/524288/1-16 6.21GB/s ± 2% 6.95GB/s ± 1% +11.95% (p=0.000 n=10+10) RepeatLarge/524288/16-16 6.24GB/s ± 2% 6.93GB/s ± 2% +11.11% (p=0.000 n=10+10) RepeatLarge/524288/4097-16 6.18GB/s ± 2% 6.82GB/s ± 1% +10.39% (p=0.000 n=9+10) RepeatLarge/1048576/1-16 5.34GB/s ± 2% 6.41GB/s ± 2% +20.05% (p=0.000 n=10+10) RepeatLarge/1048576/16-16 5.33GB/s ± 1% 6.45GB/s ± 2% +20.84% (p=0.000 n=10+9) RepeatLarge/1048576/4097-16 5.28GB/s ± 1% 6.17GB/s ± 2% +16.75% (p=0.000 n=10+10) RepeatLarge/2097152/1-16 4.04GB/s ± 1% 6.21GB/s ± 1% +53.89% (p=0.000 n=9+8) RepeatLarge/2097152/16-16 4.02GB/s ± 1% 6.20GB/s ± 2% +54.37% (p=0.000 n=10+9) RepeatLarge/2097152/4097-16 4.94GB/s ± 1% 6.04GB/s ± 1% +22.36% (p=0.000 n=10+10) RepeatLarge/4194304/1-16 3.10GB/s ± 1% 5.74GB/s ± 0% +85.04% (p=0.000 n=10+9) RepeatLarge/4194304/16-16 3.10GB/s ± 2% 5.72GB/s ± 1% +84.26% (p=0.000 n=9+10) RepeatLarge/4194304/4097-16 3.03GB/s ± 4% 5.61GB/s ± 1% +85.06% (p=0.000 n=10+9) RepeatLarge/8388608/1-16 3.08GB/s ± 2% 6.25GB/s ± 1% +103.09% (p=0.000 n=9+9) RepeatLarge/8388608/16-16 3.07GB/s ± 2% 6.26GB/s ± 3% +104.07% (p=0.000 n=10+9) RepeatLarge/8388608/4097-16 3.08GB/s ± 2% 6.23GB/s ± 2% +102.09% (p=0.000 n=9+10) RepeatLarge/16777216/1-16 3.25GB/s ± 2% 5.78GB/s ± 3% +78.03% (p=0.000 n=9+9) RepeatLarge/16777216/16-16 3.25GB/s ± 1% 5.75GB/s ± 1% +77.21% (p=0.000 n=9+10) RepeatLarge/16777216/4097-16 3.29GB/s ± 3% 5.72GB/s ± 2% +73.74% (p=0.000 n=10+10) RepeatLarge/33554432/1-16 3.68GB/s ± 2% 5.90GB/s ± 1% +60.20% (p=0.000 n=10+10) RepeatLarge/33554432/16-16 3.69GB/s ± 3% 5.88GB/s ± 1% +59.54% (p=0.000 n=10+9) RepeatLarge/33554432/4097-16 3.74GB/s ± 1% 5.94GB/s ± 2% +58.68% (p=0.000 n=7+10) RepeatLarge/67108864/1-16 4.62GB/s ±12% 6.11GB/s ± 3% +32.23% (p=0.000 n=10+9) RepeatLarge/67108864/16-16 4.77GB/s ± 2% 6.09GB/s ± 2% +27.88% (p=0.000 n=9+9) RepeatLarge/67108864/4097-16 4.78GB/s ± 1% 6.19GB/s ± 1% +29.51% (p=0.000 n=9+10) RepeatLarge/134217728/1-16 4.60GB/s ±16% 6.52GB/s ± 9% +41.67% (p=0.000 n=10+10) RepeatLarge/134217728/16-16 4.80GB/s ± 4% 6.81GB/s ± 2% +41.82% (p=0.000 n=10+9) RepeatLarge/134217728/4097-16 4.79GB/s ± 4% 6.81GB/s ± 2% +42.31% (p=0.000 n=9+10) RepeatLarge/268435456/1-16 4.43GB/s ±25% 6.27GB/s ±14% +41.52% (p=0.000 n=10+10) RepeatLarge/268435456/16-16 4.75GB/s ± 4% 6.68GB/s ± 4% +40.50% (p=0.000 n=9+10) RepeatLarge/268435456/4097-16 4.75GB/s ± 3% 6.58GB/s ± 4% +38.68% (p=0.000 n=9+10) RepeatLarge/536870912/1-16 4.96GB/s ± 9% 6.39GB/s ±16% +28.90% (p=0.000 n=8+10) RepeatLarge/536870912/16-16 4.66GB/s ± 6% 6.57GB/s ± 7% +40.82% (p=0.000 n=10+9) RepeatLarge/536870912/4097-16 4.68GB/s ±11% 6.88GB/s ± 3% +47.01% (p=0.000 n=10+9) RepeatLarge/1073741824/1-16 4.39GB/s ±23% 6.57GB/s ± 5% +49.75% (p=0.000 n=10+8) RepeatLarge/1073741824/16-16 4.73GB/s ±13% 6.89GB/s ± 1% +45.68% (p=0.000 n=9+8) RepeatLarge/1073741824/4097-16 4.97GB/s ±15% 6.73GB/s ± 9% +35.45% (p=0.000 n=10+10) The results above come from a Intel i9-9980HK (256KB L2) with TurboBoost disabled. Change-Id: I79dd57da0429aee9020ffd7bc458a034b999b740 Reviewed-on: https://go-review.googlesource.com/c/go/+/419054 Reviewed-by: Ian Lance Taylor <iant@google.com> Auto-Submit: Ian Lance Taylor <iant@google.com> Run-TryBot: Ian Lance Taylor <iant@google.com> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com> TryBot-Result: Gopher Robot <gobot@golang.org>
Diffstat (limited to 'src/strings')
-rw-r--r--src/strings/strings.go42
-rw-r--r--src/strings/strings_test.go24
2 files changed, 58 insertions, 8 deletions
diff --git a/src/strings/strings.go b/src/strings/strings.go
index fee161e4cc..646161fdda 100644
--- a/src/strings/strings.go
+++ b/src/strings/strings.go
@@ -520,8 +520,8 @@ func Map(mapping func(rune) rune, s string) string {
// Repeat returns a new string consisting of count copies of the string s.
//
-// It panics if count is negative or if
-// the result of (len(s) * count) overflows.
+// It panics if count is negative or if the result of (len(s) * count)
+// overflows.
func Repeat(s string, count int) string {
switch count {
case 0:
@@ -533,24 +533,50 @@ func Repeat(s string, count int) string {
// Since we cannot return an error on overflow,
// we should panic if the repeat will generate
// an overflow.
- // See Issue golang.org/issue/16237
+ // See golang.org/issue/16237.
if count < 0 {
panic("strings: negative Repeat count")
} else if len(s)*count/count != len(s) {
panic("strings: Repeat count causes overflow")
}
+ if len(s) == 0 {
+ return ""
+ }
+
n := len(s) * count
+
+ // Past a certain chunk size it is counterproductive to use
+ // larger chunks as the source of the write, as when the source
+ // is too large we are basically just thrashing the CPU D-cache.
+ // So if the result length is larger than an empirically-found
+ // limit (8KB), we stop growing the source string once the limit
+ // is reached and keep reusing the same source string - that
+ // should therefore be always resident in the L1 cache - until we
+ // have completed the construction of the result.
+ // This yields significant speedups (up to +100%) in cases where
+ // the result length is large (roughly, over L2 cache size).
+ const chunkLimit = 8 * 1024
+ chunkMax := n
+ if n > chunkLimit {
+ chunkMax = chunkLimit / len(s) * len(s)
+ if chunkMax == 0 {
+ chunkMax = len(s)
+ }
+ }
+
var b Builder
b.Grow(n)
b.WriteString(s)
for b.Len() < n {
- if b.Len() <= n/2 {
- b.WriteString(b.String())
- } else {
- b.WriteString(b.String()[:n-b.Len()])
- break
+ chunk := n - b.Len()
+ if chunk > b.Len() {
+ chunk = b.Len()
+ }
+ if chunk > chunkMax {
+ chunk = chunkMax
}
+ b.WriteString(b.String()[:chunk])
}
return b.String()
}
diff --git a/src/strings/strings_test.go b/src/strings/strings_test.go
index 210bd9e44b..27489c2d16 100644
--- a/src/strings/strings_test.go
+++ b/src/strings/strings_test.go
@@ -1105,6 +1105,8 @@ func TestCaseConsistency(t *testing.T) {
*/
}
+var longString = "a" + string(make([]byte, 1<<16)) + "z"
+
var RepeatTests = []struct {
in, out string
count int
@@ -1116,6 +1118,9 @@ var RepeatTests = []struct {
{"-", "-", 1},
{"-", "----------", 10},
{"abc ", "abc abc abc ", 3},
+ // Tests for results over the chunkLimit
+ {string(rune(0)), string(make([]byte, 1<<16)), 1 << 16},
+ {longString, longString + longString, 2},
}
func TestRepeat(t *testing.T) {
@@ -1885,6 +1890,25 @@ func BenchmarkRepeat(b *testing.B) {
}
}
+func BenchmarkRepeatLarge(b *testing.B) {
+ s := Repeat("@", 8*1024)
+ for j := 8; j <= 30; j++ {
+ for _, k := range []int{1, 16, 4097} {
+ s := s[:k]
+ n := (1 << j) / k
+ if n == 0 {
+ continue
+ }
+ b.Run(fmt.Sprintf("%d/%d", 1<<j, k), func(b *testing.B) {
+ for i := 0; i < b.N; i++ {
+ Repeat(s, n)
+ }
+ b.SetBytes(int64(n * len(s)))
+ })
+ }
+ }
+}
+
func BenchmarkIndexAnyASCII(b *testing.B) {
x := Repeat("#", 2048) // Never matches set
cs := "0123456789abcdefghijklmnopqrstuvwxyz0123456789abcdefghijklmnopqrstuvwxyz"
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