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runtime/cgo: store M for C-created thread in pthread key

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In a C thread, it's necessary to acquire an extra M by using needm while invoking a Go function from C. But, needm and dropm are heavy costs due to the signal-related syscalls.
So, we change to not dropm while returning back to C, which means binding the extra M to the C thread until it exits, to avoid needm and dropm on each C to Go call.
Instead, we only dropm while the C thread exits, so the extra M won't leak.

When invoking a Go function from C:
Allocate a pthread variable using pthread_key_create, only once per shared object, and register a thread-exit-time destructor.
And store the g0 of the current m into the thread-specified value of the pthread key,  only once per C thread, so that the destructor will put the extra M back onto the extra M list while the C thread exits.

When returning back to C:
Skip dropm in cgocallback, when the pthread variable has been created, so that the extra M will be reused the next time invoke a Go function from C.

This is purely a performance optimization. The old version, in which needm & dropm happen on each cgo call, is still correct too, and we have to keep the old version on systems with cgo but without pthreads, like Windows.

This optimization is significant, and the specific value depends on the OS system and CPU, but in general, it can be considered as 10x faster, for a simple Go function call from a C thread.

For the newly added BenchmarkCGoInCThread, some benchmark results:
1. it's 28x faster, from 3395 ns/op to 121 ns/op, in darwin OS & Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
2. it's 6.5x faster, from 1495 ns/op to 230 ns/op, in Linux OS & Intel(R) Xeon(R) CPU E5-2630 0 @ 2.30GHz

Fixes #51676

Change-Id: I380702fe2f9b6b401b2d6f04b0aba990f4b9ee6c
GitHub-Last-Rev: 93dc64ad98
GitHub-Pull-Request: golang/go#51679
Reviewed-on: https://go-review.googlesource.com/c/go/+/392854
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: thepudds <thepudds1460@gmail.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
This commit is contained in:
doujiang24 2023-03-24 01:30:46 +00:00 • committed by Cherry Mui
parent a6c382eaa8
commit ef0dedce87
37 changed files with 760 additions and 61 deletions
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16
src/runtime/signal_unix.go
View file

@ -435,7 +435,7 @@ func sigtrampgo(sig uint32, info *siginfo, ctx unsafe.Pointer) {
c := &sigctxt{info, ctx}
gp := sigFetchG(c)
setg(gp)
if gp == nil {
if gp == nil || (gp.m != nil && gp.m.isExtraInC) {
if sig == _SIGPROF {
// Some platforms (Linux) have per-thread timers, which we use in
// combination with the process-wide timer. Avoid double-counting.
@ -458,7 +458,18 @@ func sigtrampgo(sig uint32, info *siginfo, ctx unsafe.Pointer) {
return
}
c.fixsigcode(sig)
// Set g to nil here and badsignal will use g0 by needm.
// TODO: reuse the current m here by using the gsignal and adjustSignalStack,
// since the current g maybe a normal goroutine and actually running on the signal stack,
// it may hit stack split that is not expected here.
if gp != nil {
setg(nil)
}
badsignal(uintptr(sig), c)
// Restore g
if gp != nil {
setg(gp)
}
return
}
@ -1121,8 +1132,9 @@ func sigfwdgo(sig uint32, info *siginfo, ctx unsafe.Pointer) bool {
// (1) we weren't in VDSO page,
// (2) we were in a goroutine (i.e., m.curg != nil), and
// (3) we weren't in CGO.
// (4) we weren't in dropped extra m.
gp := sigFetchG(c)
if gp != nil && gp.m != nil && gp.m.curg != nil && !gp.m.incgo {
if gp != nil && gp.m != nil && gp.m.curg != nil && !gp.m.isExtraInC && !gp.m.incgo {
return false
}