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internal/trace: reduce event size by packing goroutine statuses

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The trace parser was using an otherwise-unused event argument to hold an
extra goroutine state argument for the GoStatus & GoStatusStack events.
This is needed because the execution tracer just records the "after" for
state transitions, but we want to have both the "before" and "after"
states available in the StateTransition info for the parsed event. When
GoStatusStack was added, the size of the argument array was increased to
still have room for the extra status. However, statuses are currently
only 1 byte, and the status argument is 8 bytes, so there is plenty of
room to pack the "before" and "after" statuses in a single argument. Do
that instead to avoid the need for an extra argument.

Change-Id: I6886eeb14fb8e5e046b6afcc5b19e04218bcacd4
Reviewed-on: https://go-review.googlesource.com/c/go/+/601455
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
This commit is contained in:
Nick Ripley 2024-07-26 15:16:24 -04:00 committed by Gopher Robot
parent 8173a29aaa
commit 705f9848ef
3 changed files with 5 additions and 8 deletions
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6
src/internal/trace/base.go
View File

@ -19,11 +19,7 @@ import (
// maxArgs is the maximum number of arguments for "plain" events,
// i.e. anything that could reasonably be represented as a baseEvent.
//
// TODO(mknyszek): This is only 6 instead of 5 because GoStatusStack
// has 5 arguments and needs to smuggle in a 6th. Figure out a way to
// shrink this in the future.
const maxArgs = 6
const maxArgs = 5
// timedEventArgs is an array that is able to hold the arguments for any
// timed event.

5
src/internal/trace/event.go
View File

@ -647,8 +647,9 @@ func (e Event) StateTransition() StateTransition {
s = goStateTransition(e.ctx.G, GoSyscall, GoRunnable)
s.Stack = e.Stack() // This event references the resource the event happened on.
case go122.EvGoStatus, go122.EvGoStatusStack:
// N.B. ordering.advance populates e.base.extra.
s = goStateTransition(GoID(e.base.args[0]), GoState(e.base.extra(version.Go122)[0]), go122GoStatus2GoState[e.base.args[2]])
packedStatus := e.base.args[2]
from, to := packedStatus>>32, packedStatus&((1<<32)-1)
s = goStateTransition(GoID(e.base.args[0]), GoState(from), go122GoStatus2GoState[to])
default:
panic(fmt.Sprintf("internal error: unexpected event type for StateTransition kind: %s", go122.EventString(e.base.typ)))
}

2
src/internal/trace/order.go
View File

@ -377,7 +377,7 @@ func (o *ordering) advanceGoStatus(ev *baseEvent, evt *evTable, m ThreadID, gen
} else {
return curCtx, false, fmt.Errorf("found goroutine status for new goroutine after the first generation: id=%v status=%v", gid, status)
}
ev.extra(version.Go122)[0] = uint64(oldState) // Smuggle in the old state for StateTransition.
ev.args[2] = uint64(oldState)<<32 | uint64(status) // Smuggle in the old state for StateTransition.
newCtx := curCtx
switch status {