31437f25f2
Checking whether the current allocation needs to be profiled is currently branch-y and weirdly a lot of code. The branches are generally predictable, but it's a surprising number of instructions. Part of the problem is that MemProfileRate is just a global that can be set at any time, so we need to load it and check certain settings explicitly. In an ideal world, we would just always subtract from nextSample and have a single branch to take the slow path if we subtract below zero. If MemProfileRate were a function, we could trash all the nextSample values intentionally in each mcache. This would be slow, but MemProfileRate changes rarely while the malloc hot path is well, hot. Unfortunate... Although this ideal world is, AFAICT, impossible, we can still get close. If we cache the value of MemProfileRate in each mcache, then we can force malloc to take the slow path whenever MemProfileRate changes. This does require two additional loads, but crucially, these loads are independent of everything else in mallocgc. Furthermore, the branch dependent on those loads is incredibly predictable in practice. This CL on its own has little-to-no impact on mallocgc. But this codepath is going to be duplicated in several places in the next CL, so it'll pay to simplify it. Also, we're very much trying to remedy a death-by-a-thousand-cuts situation, and malloc is currently still kind of a monster -- it will not help if mallocgc isn't really streamlined itself. Lastly, there's a nice property now that all nextSample values get immediately re-sampled when MemProfileRate changes. Change-Id: I6443d0cf9bd7861595584442b675ac1be8ea3455 Reviewed-on: https://go-review.googlesource.com/c/go/+/615815 LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Auto-Submit: Michael Knyszek <mknyszek@google.com> Reviewed-by: Keith Randall <khr@golang.org> Reviewed-by: Keith Randall <khr@google.com> |
||
|---|---|---|
| .github | ||
| api | ||
| doc | ||
| lib | ||
| misc | ||
| src | ||
| test | ||
| .gitattributes | ||
| .gitignore | ||
| codereview.cfg | ||
| CONTRIBUTING.md | ||
| go.env | ||
| LICENSE | ||
| PATENTS | ||
| README.md | ||
| 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 4.0 Attribution 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://go.dev/dl/.
After downloading a binary release, visit https://go.dev/doc/install for installation instructions.
Install From Source
If a binary distribution is not available for your combination of operating system and architecture, visit https://go.dev/doc/install/source for source installation instructions.
Contributing
Go is the work of thousands of contributors. We appreciate your help!
To contribute, please read the contribution guidelines at https://go.dev/doc/contribute.
Note that the Go project uses the issue tracker for bug reports and proposals only. See https://go.dev/wiki/Questions for a list of places to ask questions about the Go language.