67c2dcbc59
This change modifies the implementation of (*mspan).countAlloc by using OnesCount64 (which on many systems is intrinsified). It does so by using an unsafe pointer cast, but in this case we don't care about endianness because we're just counting bits set. This change means we no longer need the popcnt table which was redundant in the runtime anyway. We can also simplify the logic here significantly by observing that mark bits allocations are always 8-byte aligned, so we don't need to handle any edge-cases due to the fact that OnesCount64 operates on 64 bits at a time: all irrelevant bits will be zero. Overall, this implementation is significantly faster than the old one on amd64, and should be similarly faster (or better!) on other systems which support the intrinsic. On systems which do not, it should be roughly the same performance because OnesCount64 is implemented using a table in the general case. Results on linux/amd64: name old time/op new time/op delta MSpanCountAlloc/bits=64-4 16.8ns ± 0% 12.7ns ± 0% -24.40% (p=0.000 n=5+4) MSpanCountAlloc/bits=128-4 23.5ns ± 0% 12.8ns ± 0% -45.70% (p=0.000 n=4+5) MSpanCountAlloc/bits=256-4 43.5ns ± 0% 12.8ns ± 0% -70.67% (p=0.000 n=4+5) MSpanCountAlloc/bits=512-4 59.5ns ± 0% 15.4ns ± 0% -74.12% (p=0.008 n=5+5) MSpanCountAlloc/bits=1024-4 116ns ± 1% 23ns ± 0% -79.84% (p=0.000 n=5+4) Change-Id: Id4c994be22224653af5333683a69b0937130ed04 Reviewed-on: https://go-review.googlesource.com/c/go/+/216558 Run-TryBot: Michael Knyszek <mknyszek@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Austin Clements <austin@google.com> Reviewed-by: Keith Randall <khr@golang.org> |
||
|---|---|---|
| .github | ||
| api | ||
| doc | ||
| lib/time | ||
| misc | ||
| src | ||
| test | ||
| .gitattributes | ||
| .gitignore | ||
| AUTHORS | ||
| CONTRIBUTING.md | ||
| CONTRIBUTORS | ||
| favicon.ico | ||
| LICENSE | ||
| PATENTS | ||
| README.md | ||
| robots.txt | ||
| SECURITY.md | ||
The Go Programming Language
Go is an open source programming language that makes it easy to build simple, reliable, and efficient software.
Gopher image by Renee French, licensed under Creative Commons 3.0 Attributions license.
Our canonical Git repository is located at https://go.googlesource.com/go. There is a mirror of the repository at https://github.com/golang/go.
Unless otherwise noted, the Go source files are distributed under the BSD-style license found in the LICENSE file.
Download and Install
Binary Distributions
Official binary distributions are available at https://golang.org/dl/.
After downloading a binary release, visit https://golang.org/doc/install or load doc/install.html in your web browser for installation instructions.
Install From Source
If a binary distribution is not available for your combination of operating system and architecture, visit https://golang.org/doc/install/source or load doc/install-source.html in your web browser for source installation instructions.
Contributing
Go is the work of thousands of contributors. We appreciate your help!
To contribute, please read the contribution guidelines: https://golang.org/doc/contribute.html
Note that the Go project uses the issue tracker for bug reports and proposals only. See https://golang.org/wiki/Questions for a list of places to ask questions about the Go language.