On Sun, Mar 14, 2021 at 12:00 PM Robert Engels <reng...@ix.netcom.com> wrote: > > Based on two decades of Java FFI - the overhead comes from type mapping not > the housekeeping to control GC. The latter can be as simple as a volatile > read and 2 writes per call and can usually be coalesced in tight loops. Since > Go already has easy native C type mapping the FFi should be very efficient > depending on types used.
Go and Java are pretty different here. The type mapping overhead from Go to C is effectively non-existent--or, to put it another way, it's pushed entirely onto the programmer The GC housekeeping is, as you say, low. The heaviest cost is the scheduling housekeeping: notifying the scheduler that the goroutine is entering a new scheduling regime, so that a blocking call in C does not block the entire program. A minor cost is the change is the calling convention. As Jason says, if all of the C code--and I really do mean all--can be compiled by a Go-aware C compiler, then the scheduling overhead can be largely eliminated, and pushed into the system call interface much as is done for Go code. But that is a heavy lift. Compiling only some of the C code with a Go-aware C compiler seems unlikely to provide any significant benefit. Ian > On Mar 14, 2021, at 11:37 AM, Jason E. Aten <j.e.a...@gmail.com> wrote: > > > I'm no authority here, but I believe a large (major?) part of the Cgo > overhead is caused by scheduling overhead. As I understand it, a C function > call is non-preemptible and the Go runtime don't know whether the call will > block. > > But that part would be handled by the C-compiler-that-knows-Go inserting the > pre-emption points just like the Go compiler does into the generated code. Or > the same checks for blocking. > > -- > You received this message because you are subscribed to the Google Groups > "golang-nuts" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to golang-nuts+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/golang-nuts/0ac6ac9e-ed99-4536-a8b0-44674f8b85a5n%40googlegroups.com. > > -- > You received this message because you are subscribed to the Google Groups > "golang-nuts" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to golang-nuts+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/golang-nuts/47869391-FC69-44C8-A7AA-8F335A17CF71%40ix.netcom.com. -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/CAOyqgcVSphZ4w%2BNaCFnkHOmoZ%2BOdD-Ob3K%2BbcjVn02fivJRX%2Bg%40mail.gmail.com.
