A previous PR made it so that the Go 1.17 collector locked only around
uses of rmSampleBuf, but really that means that Metric values may be
sent over the channel containing some values from future metrics.Read
calls. While generally-speaking this isn't a problem, we lose any
consistency guarantees provided by the runtime/metrics package.
Also, that optimization to not just lock around all of Collect was
premature. Truthfully, Collect is called relatively infrequently, and
its critical path is fairly fast (10s of µs). To prove it, this change
also adds a benchmark.
name old time/op new time/op delta
GoCollector-16 43.7µs ± 2% 43.2µs ± 2% ~ (p=0.190 n=9+9)
Note that because the benchmark is single-threaded it actually looks
like it might be getting *slightly* faster, because all those Collect
calls for the Metrics are direct calls instead of interface calls.
Signed-off-by: Michael Anthony Knyszek <mknyszek@google.com>
This change introduces use of the runtime/metrics package in place of
runtime.MemStats for Go 1.17 or later. The runtime/metrics package was
introduced in Go 1.16, but not all the old metrics were accounted for
until 1.17.
The runtime/metrics package offers several advantages over using
runtime.MemStats:
* The list of metrics and their descriptions are machine-readable,
allowing new metrics to get added without any additional work.
* Detailed histogram-based metrics are now available, offering much
deeper insights into the Go runtime.
* The runtime/metrics API is significantly more efficient than
runtime.MemStats, even with the additional metrics added, because
it does not require any stop-the-world events.
That being said, integrating the package comes with some caveats, some
of which were discussed in #842. Namely:
* The old MemStats-based metrics need to continue working, so they're
exported under their old names backed by equivalent runtime/metrics
metrics.
* Earlier versions of Go need to continue working, so the old code
remains, but behind a build tag.
Finally, a few notes about the implementation:
* This change includes a whole bunch of refactoring to avoid significant
code duplication.
* This change adds a new histogram metric type specifically optimized
for runtime/metrics histograms. This type's methods also include
additional logic to deal with differences in bounds conventions.
* This change makes a whole bunch of decisions about how runtime/metrics
names are translated.
* This change adds a `go generate` script to generate a list of expected
runtime/metrics names for a given Go version for auditing. Users of
new versions of Go will transparently be allowed to use new metrics,
however.
Signed-off-by: Michael Anthony Knyszek <mknyszek@google.com>
Michael Knyszek