d7941030c9
Currently the GC CPU limiter consumes CPU time from a few pools, but because the events that flush to those pools may overlap, rather than be strictly contained within, the update window for the GC CPU limiter, the limiter's accounting is ultimately sloppy. This sloppiness complicates accounting for idle time more completely, and makes reasoning about the transient behavior of the GC CPU limiter much more difficult. To remedy this, this CL adds a field to the P struct that tracks the start time of any in-flight event the limiter might care about, along with information about the nature of that event. This timestamp is managed atomically so that the GC CPU limiter can come in and perform a read of the partial CPU time consumed by a given event. The limiter also updates the timestamp so that only what's left over is flushed by the event itself when it completes. The end result of this change is that, since the GC CPU limiter is aware of all past completed events, and all in-flight events, it can much more accurately collect the CPU time of events since the last update. There's still the possibility for skew, but any leftover time will be captured in the following update, and the magnitude of this leftover time is effectively bounded by the update period of the GC CPU limiter, which is much easier to consider. One caveat of managing this timestamp-type combo atomically is that they need to be packed in 64 bits. So, this CL gives up the top 3 bits of the timestamp and places the type information there. What this means is we effectively have only a 61-bit resolution timestamp. This is fine when the top 3 bits are the same between calls to nanotime, but becomes a problem on boundaries when those 3 bits change. These cases may cause hiccups in the GC CPU limiter by not accounting for some source of CPU time correctly, but with 61 bits of resolution this should be extremely rare. The rate of update is on the order of milliseconds, so at worst the runtime will be off of any given measurement by only a few CPU-milliseconds (and this is directly bounded by the rate of update). We're probably more inaccurate from the fact that we don't measure real CPU time but only approximate it. For #52890. Change-Id: I347f30ac9e2ba6061806c21dfe0193ef2ab3bbe9 Reviewed-on: https://go-review.googlesource.com/c/go/+/410120 Reviewed-by: Michael Pratt <mpratt@google.com> Run-TryBot: Michael Knyszek <mknyszek@google.com> TryBot-Result: Gopher Robot <gobot@golang.org> |
||
|---|---|---|
| .github | ||
| api | ||
| doc | ||
| lib/time | ||
| misc | ||
| src | ||
| test | ||
| .gitattributes | ||
| .gitignore | ||
| AUTHORS | ||
| codereview.cfg | ||
| CONTRIBUTING.md | ||
| CONTRIBUTORS | ||
| 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 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://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.