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The runtime tracer currently uses a per-M seqlock to indicate whether a
thread is writing to a local trace buffer. The seqlock is updated with
two atomic adds, read-modify-write operations. These are quite
expensive, even though they're completely uncontended.
We can make these operations slightly cheaper by using an atomic store.
The key insight here is that only one thread ever writes to the value at
a time, so only the "write" of the read-modify-write actually matters.
At that point, it doesn't really matter that we have a monotonically
increasing counter. This is made clearer by the fact that nothing other
than basic checks make sure the counter is monotonically increasing:
everything only depends on whether the counter is even or odd.
At that point, all we really need is a flag: an atomic.Bool, which we
can update with an atomic Store, a write-only instruction.
Change-Id: I0cfe39b34c7634554c34c53c0f0e196d125bbc4a
Reviewed-on: https://go-review.googlesource.com/c/go/+/721840
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
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Found by github.com/mdempsky/unconvert
Change-Id: Ib78cceb718146509d96dbb6da87b27dbaeba1306
GitHub-Last-Rev: dedf354811701ce8920c305b6f7aa78914a4171c
GitHub-Pull-Request: golang/go#74771
Reviewed-on: https://go-review.googlesource.com/c/go/+/690735
Reviewed-by: Mark Freeman <mark@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
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This change deduplicates trace wire format definitions between the
runtime and the trace parser by making the internal/trace/tracev2
package the source of truth.
Change-Id: Ia0721d3484a80417e40ac473ec32870bee73df09
Reviewed-on: https://go-review.googlesource.com/c/go/+/644221
Auto-Submit: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
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This change renames the v2 execution tracer files created as part of
Updates #66703
For #60773
Change-Id: I91bfdc08fec4ec68ff3a6e8b5c86f6f8bcae6e6d
Reviewed-on: https://go-review.googlesource.com/c/go/+/576257
Auto-Submit: Carlos Amedee <carlos@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
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